diff --git a/Example/ForeFlightKMLDemo/KML/KMLGenerator.swift b/Example/ForeFlightKMLDemo/KML/KMLGenerator.swift
index a12f5eb..e328461 100644
--- a/Example/ForeFlightKMLDemo/KML/KMLGenerator.swift
+++ b/Example/ForeFlightKMLDemo/KML/KMLGenerator.swift
@@ -4,7 +4,7 @@ import CoreLocation
 import ForeFlightKML
 
 enum KMLGenerator {
-    static func generateCircleKML(center: CLLocationCoordinate2D, radiusMeters: Double) throws -> Data? {
+    static func generateCircleKML(center: CLLocationCoordinate2D, radiusMeters: Double) throws -> BuildResult {
         let builder = ForeFlightKMLBuilder(documentName: "Foreflight KML Demo")
 
         let centerCoordinate = Coordinate(latitude: center.latitude, longitude: center.longitude)
@@ -23,7 +23,7 @@ enum KMLGenerator {
             radiusMeters: radiusMeters * 2,
             style: PolygonStyle(outlineColor: .black, fillColor: .warning.withAlpha(0.3)))
 
-        return try builder.buildKMZ()
+        return try builder.build(as: .kmz)
 
     }
 
diff --git a/Example/ForeFlightKMLDemo/Views/ContentView.swift b/Example/ForeFlightKMLDemo/Views/ContentView.swift
index 80f2ab4..fda51f8 100644
--- a/Example/ForeFlightKMLDemo/Views/ContentView.swift
+++ b/Example/ForeFlightKMLDemo/Views/ContentView.swift
@@ -1,5 +1,6 @@
 import SwiftUI
 import MapKit
+import ForeFlightKML
 
 struct ContentView: View {
     @State private var lastTapCoordinate: CLLocationCoordinate2D?
@@ -49,14 +50,14 @@ struct ContentView: View {
     private func handleMapTap(_ coord: CLLocationCoordinate2D) {
         lastTapCoordinate = coord
         do {
-            let kmz = try KMLGenerator.generateCircleKML(center: coord, radiusMeters: defaultRadiusMeters)
+            let buildResult = try KMLGenerator.generateCircleKML(center: coord, radiusMeters: defaultRadiusMeters)
 
             let dateFormatter = DateFormatter()
             dateFormatter.dateFormat = "yyyyMMdd'T'HHmmss'Z'"
 
-            let tmpURL = FileManager.default.temporaryDirectory.appendingPathComponent("\(dateFormatter.string(from: Date())).kmz")
-
-            try kmz?.write(to: tmpURL)
+            let tmpURL = FileManager.default.temporaryDirectory.appendingPathComponent("\(dateFormatter.string(from: Date())).\(buildResult.fileExtension)")
+            
+            try buildResult.data.write(to: tmpURL)
             kmlToShareURL = tmpURL
             showingShare = true
         } catch {
diff --git a/Package.swift b/Package.swift
index 71dbf62..03bc596 100644
--- a/Package.swift
+++ b/Package.swift
@@ -28,6 +28,10 @@ let package = Package(
         .testTarget(
             name: "ForeFlightKMLTests",
             dependencies: ["ForeFlightKML"]
+        ),
+        .testTarget(
+            name: "UserMapShapeTests",
+            dependencies: ["ForeFlightKML"]
         )
     ]
 )
diff --git a/README.md b/README.md
index 01277ac..eafd548 100644
--- a/README.md
+++ b/README.md
@@ -21,7 +21,7 @@ This package provides a small, focused API for composing KML/KMZ documents suita
 ## Example Output 
 Using the example given on the [ForeFlight website](https://foreflight.com/support/user-map-shapes/) the below is generated using this Framework. 
 
-See `/Tests/ForeFlightKMLTests/UserMapShapesSampleFullTest.swift`
+See `/Tests/UserMapShapeTests/UserMapShapesSampleFullTest.swift`
 
 <img width="615" height="770" alt="Image" src="/docs/example-output.png" />
 
@@ -32,6 +32,7 @@ import ForeFlightKML
 import Geodesy (used for coordinates)
 
 let builder = ForeFlightKMLBuilder(documentName: "Airport with ATZ")
+
 builder.addLine(
     name: "Runway 15-33", 
     coordinates: [Coordinate(latitude:, longitude:),Coordinate(latitude:, longitude:)],
@@ -45,8 +46,10 @@ builder.addLineCircle(
     PolygonStyle(outlineColor: .black, fillColor: .warning.withAlpha(0.3))
 )
 
-let url = FileManager.default.temporaryDirectory.appendingPathComponent("shapes.kml")
-try builder.build().write(to: url, atomically: true, encoding: .utf8)
+let buildResult = try builder.build(as: .kmz)
+
+let url = FileManager.default.temporaryDirectory.appendingPathComponent("shapes\(buildResult.fileExtension)")
+try buildResult.data.write(to: tmpURL)
 presentShareSheet(with: url)
 ```
 
@@ -59,7 +62,7 @@ presentShareSheet(with: url)
  `ForeFlightKMLBuilder` is the builder for the KML/KMZ document. 
  - Document name can be set on `init` or with `setDocumentName()` 
  - Elements can be manually added using `addPlacemark(_:)`
- - The output is accessed by: for KML `try builder.build()` or for KMZ: `try builder.buildKMZ()`
+ - The output is accessed by `try builder.build()`
 
 ### KMLBuilder Convenience Elements
  - `addPoint` Add a point with style.
@@ -73,9 +76,16 @@ presentShareSheet(with: url)
  - `addLabel` Add a text-only label placemark at a coordinate.
 
 ### ForeflightKMLBuilder Export formats
-- `kml String` via `builder.build()`
-- `kml Data` via `builder.kmlData()`
-- `kmz Data` via `builder.buildKMZ()` 
+Type `BuildResult` contains: 
+``` 
+    data: Data
+    fileExtension: String
+    mimetype: String
+```
+Specific data access: 
+- `kml Data` via `builder.build(as: .kml)`
+- `kmz Data` via `builder.build(as: .kmz)`
+- `kml String` via `builder.kmlString()` note: this can be unsafe and should only be used for debugging
 - KMZ (zipped KML) is required when using custom icons or using labelBadge (which uses a transparent .png under the hood). 
 
 ### Underlying elements
@@ -96,7 +106,7 @@ Full public API surface is visible in the package sources.
 
 ## Demo & tests
 
-The repo contains an `Example` app that demonstrates building shapes and the `Tests` folder with unit tests. 
+The repo contains an `Example` app that demonstrates building shapes and the `Tests` folder with unit and end to end example tests. 
 
 ## Contributing
 
diff --git a/Sources/ForeFlightKML/Enums/OutputFormat.swift b/Sources/ForeFlightKML/Enums/OutputFormat.swift
new file mode 100644
index 0000000..5ead170
--- /dev/null
+++ b/Sources/ForeFlightKML/Enums/OutputFormat.swift
@@ -0,0 +1,4 @@
+public enum OutputFormat {
+    case kml
+    case kmz
+}
diff --git a/Sources/ForeFlightKML/Errors/BuildError.swift b/Sources/ForeFlightKML/Errors/BuildError.swift
new file mode 100644
index 0000000..967a09b
--- /dev/null
+++ b/Sources/ForeFlightKML/Errors/BuildError.swift
@@ -0,0 +1,19 @@
+enum BuildError: Error, Equatable {
+    case missingAssetsForKMZ
+    case unsupportedFeatureForKML
+    case emptyArchive
+    case internalError(underlying: Error)
+
+    static func == (lhs: BuildError, rhs: BuildError) -> Bool {
+        switch (lhs, rhs) {
+        case (.missingAssetsForKMZ, .missingAssetsForKMZ): return true
+        case (.unsupportedFeatureForKML, .unsupportedFeatureForKML): return true
+        case (.emptyArchive, .emptyArchive): return true
+        case (.internalError, .internalError):
+            // Consider any internalError equal regardless of underlying Error
+            return true
+        default:
+            return false
+        }
+    }
+}
diff --git a/Sources/ForeFlightKML/Errors/KMZExportError.swift b/Sources/ForeFlightKML/Errors/ExportError.swift
similarity index 71%
rename from Sources/ForeFlightKML/Errors/KMZExportError.swift
rename to Sources/ForeFlightKML/Errors/ExportError.swift
index ba3e86e..2fd7800 100644
--- a/Sources/ForeFlightKML/Errors/KMZExportError.swift
+++ b/Sources/ForeFlightKML/Errors/ExportError.swift
@@ -1,4 +1,4 @@
-public enum KMZExportError: Error {
+public enum ExportError: Error {
     case kmzRequired
     case missingLocalResource(String)
     case archiveCreationFailed
diff --git a/Sources/ForeFlightKML/ForeFlightKML.swift b/Sources/ForeFlightKML/ForeFlightKML.swift
index 445d6b2..4c2a830 100644
--- a/Sources/ForeFlightKML/ForeFlightKML.swift
+++ b/Sources/ForeFlightKML/ForeFlightKML.swift
@@ -4,7 +4,7 @@ import GeodesySpherical
 /// A Builder for composing a KML Document (styles + placemarks).
 /// Use this to create KML documents compatible with ForeFlight's User Map Shapes feature.
 ///
-public final class ForeFlightKMLBuilder {
+public final class ForeFlightKMLBuilder: Building {
     /// Optional name for the `<Document>` element.
     private var documentName: String?
     /// Collection of placemarks added to this builder.
@@ -57,12 +57,30 @@ public final class ForeFlightKMLBuilder {
     /// Generate the complete KML string for this document.
     /// This method can be called multiple times - it doesn't modify the builder state.
     /// - Returns: A complete KML document as a UTF-8 string ready for export to ForeFlight
-    public func build() throws -> String {
-        guard !requiresKMZ else {
-            throw KMZExportError.kmzRequired
+    public func build(as format: OutputFormat = .kmz) throws -> BuildResult {
+        if format == .kml, requiresKMZ {
+            throw BuildError.unsupportedFeatureForKML
         }
 
-        return kmlString()
+        switch format {
+        case .kml:
+            let data = buildKML()
+            return BuildResult(
+                data: data,
+                fileExtension: "kml",
+                mimetype: "application/vnd.google-earth.kml+xml"
+            )
+
+        case .kmz:
+            guard let data = try buildKMZ() else {
+                throw BuildError.emptyArchive
+            }
+            return BuildResult(
+                data: data,
+                fileExtension: "kmz",
+                mimetype: "application/vnd.google-earth.kmz"
+            )
+        }
     }
 
     /// Produce the full KML string for this document.
@@ -91,7 +109,7 @@ public final class ForeFlightKMLBuilder {
     /// Produce the KML document as `Data` using the given text encoding.
     /// - Parameter encoding: The `String.Encoding` to use when converting the KML string into data. 
     /// - Returns: `Data` containing the encoded KML, or an empty `Data` if encoding fails.
-    public func kmlData(encoding: String.Encoding = .utf8) -> Data {
+    public func buildKML(encoding: String.Encoding = .utf8) -> Data {
         return kmlString().data(using: encoding) ?? Data()
     }
 
diff --git a/Sources/ForeFlightKML/ForeflightKML+KMZ.swift b/Sources/ForeFlightKML/ForeflightKML+KMZ.swift
index 300dac6..46cacdc 100644
--- a/Sources/ForeFlightKML/ForeflightKML+KMZ.swift
+++ b/Sources/ForeFlightKML/ForeflightKML+KMZ.swift
@@ -6,7 +6,7 @@ public extension ForeFlightKMLBuilder {
     /// Build a KMZ (ZIP) containing doc.kml and any required local assets.
     func buildKMZ() throws -> Data? {
 
-        let kmlData = kmlData()
+        let kmlData = buildKML()
 
         let archive = try Archive(accessMode: .create)
 
@@ -38,7 +38,7 @@ private extension ForeFlightKMLBuilder {
         let bundle = Bundle.module
 
         guard let iconURL = bundle.url(forResource: "1x1", withExtension: "png") else {
-            throw KMZExportError.missingLocalResource("1x1.png")
+            throw ExportError.missingLocalResource("1x1.png")
         }
 
         try archive.addEntry(
diff --git a/Sources/ForeFlightKML/Utils/DataFormat.swift b/Sources/ForeFlightKML/Utils/DataFormat.swift
new file mode 100644
index 0000000..bf80777
--- /dev/null
+++ b/Sources/ForeFlightKML/Utils/DataFormat.swift
@@ -0,0 +1,7 @@
+import Foundation
+
+public struct BuildResult {
+    public let data: Data
+    public let fileExtension: String
+    public let mimetype: String
+}
diff --git a/Sources/ForeFlightKML/Utils/Protocols.swift b/Sources/ForeFlightKML/Utils/Protocols.swift
index 3ea966d..cfa6ff8 100644
--- a/Sources/ForeFlightKML/Utils/Protocols.swift
+++ b/Sources/ForeFlightKML/Utils/Protocols.swift
@@ -26,3 +26,7 @@ public protocol KMLSubStyle {
     // These produce the inner element tags (<LineStyle>...</LineStyle>, <PolyStyle>...</PolyStyle>).
     func kmlString() -> String
 }
+
+protocol Building {
+    func build(as format: OutputFormat) throws -> BuildResult
+}
diff --git a/Tests/ForeFlightKMLTests/Builder/ForeFlightKML+BuildTests.swift b/Tests/ForeFlightKMLTests/Builder/ForeFlightKML+BuildTests.swift
new file mode 100644
index 0000000..f95b2e6
--- /dev/null
+++ b/Tests/ForeFlightKMLTests/Builder/ForeFlightKML+BuildTests.swift
@@ -0,0 +1,92 @@
+import XCTest
+import GeodesySpherical
+@testable import ForeFlightKML
+
+final class ForeFlightKMLBuildTests: XCTestCase {
+
+    func test_build_asKMZ_returnsExpectedMetadataAndHasDocKML() throws {
+        let builder = ForeFlightKMLBuilder()
+        builder.addPoint(
+            name: "Normal",
+            coordinate: Coordinate(latitude: 51.0, longitude: -1.0),
+            altitude: 0,
+            style: PointStyle(icon: .custom(type: .square, color: .white, scale: 1.0))
+        )
+
+        let result = try builder.build(as: .kmz)
+        XCTAssertEqual(result.fileExtension, "kmz")
+        XCTAssertEqual(result.mimetype, "application/vnd.google-earth.kmz")
+        // Quick sanity check that archive contains doc.kml
+        let archive = try ArchiveDataVerifier.archive(from: result.data)
+        XCTAssertNotNil(archive["doc.kml"], "KMZ must contain doc.kml at root")
+    }
+
+    func test_build_asKML_whenNoKMZRequired_succeedsWithMetadata() throws {
+        let builder = ForeFlightKMLBuilder()
+        // Use a simple predefined icon that should not require local assets
+        builder.addPoint(
+            name: "Simple",
+            coordinate: Coordinate(latitude: 0, longitude: 0)
+        )
+
+        XCTAssertFalse(builder.requiresKMZ)
+        let result = try builder.build(as: .kml)
+        XCTAssertEqual(result.fileExtension, "kml")
+        XCTAssertEqual(result.mimetype, "application/vnd.google-earth.kml+xml")
+        // Resulting data should decode as UTF-8 and contain KML root
+        let kml = String(data: result.data, encoding: .utf8)
+        XCTAssertNotNil(kml)
+        XCTAssertTrue(kml?.contains("<kml ") == true)
+    }
+
+    func test_build_asKML_whenKMZRequired_throwsUnsupportedFeature() {
+        let builder = ForeFlightKMLBuilder()
+        // addLabel uses a local 1x1.png badge and therefore requires KMZ
+        builder.addLabel("Badge", coordinate: Coordinate(latitude: 1, longitude: 1), color: .warning)
+        XCTAssertTrue(builder.requiresKMZ)
+
+        XCTAssertThrowsError(try builder.build(as: .kml)) { error in
+            guard let buildError = error as? BuildError else {
+                return XCTFail("Expected BuildError.unsupportedFeatureForKML, got: \(error)")
+            }
+            XCTAssertEqual(buildError, .unsupportedFeatureForKML)
+        }
+    }
+
+    func test_setDocumentName_reflectedInOutput() {
+        let builder = ForeFlightKMLBuilder()
+        builder.setDocumentName("My Doc")
+        builder.addPoint(name: "p", coordinate: Coordinate(latitude: 0, longitude: 0))
+
+        let kml = builder.kmlString()
+        XCTAssertTrue(kml.contains("<name>My Doc</name>"))
+    }
+
+    func test_clear_resetsState_counts_and_requiresKMZ() {
+        let builder = ForeFlightKMLBuilder()
+        builder.addPoint(name: "p", coordinate: Coordinate(latitude: 0, longitude: 0))
+        builder.addLabel("Badge", coordinate: Coordinate(latitude: 1, longitude: 1), color: .warning)
+
+        XCTAssertGreaterThan(builder.placemarkCount, 0)
+        XCTAssertGreaterThan(builder.styleCount, 0)
+        XCTAssertTrue(builder.requiresKMZ)
+
+        builder.clear()
+
+        XCTAssertEqual(builder.placemarkCount, 0)
+        XCTAssertEqual(builder.styleCount, 0)
+        XCTAssertFalse(builder.requiresKMZ)
+    }
+}
+
+// MARK: - Local helper
+import ZIPFoundation
+private enum ArchiveDataVerifier {
+    static func archive(from data: Data) throws -> Archive {
+        let url = FileManager.default.temporaryDirectory
+            .appendingPathComponent(UUID().uuidString)
+            .appendingPathExtension("kmz")
+        try data.write(to: url)
+        return try Archive(url: url, accessMode: .read)
+    }
+}
diff --git a/Tests/ForeFlightKMLTests/ForeFlightKML+KMZTests.swift b/Tests/ForeFlightKMLTests/Builder/ForeFlightKML+KMZTests.swift
similarity index 100%
rename from Tests/ForeFlightKMLTests/ForeFlightKML+KMZTests.swift
rename to Tests/ForeFlightKMLTests/Builder/ForeFlightKML+KMZTests.swift
diff --git a/Tests/ForeFlightKMLTests/ForeFlightKMLTests.swift b/Tests/ForeFlightKMLTests/Builder/ForeFlightKMLTests.swift
similarity index 100%
rename from Tests/ForeFlightKMLTests/ForeFlightKMLTests.swift
rename to Tests/ForeFlightKMLTests/Builder/ForeFlightKMLTests.swift
diff --git a/Tests/ForeFlightKMLTests/CoreElementTests/PolygonTests.swift b/Tests/ForeFlightKMLTests/CoreElementTests/PolygonTests.swift
index a9b0e83..1f7ceea 100644
--- a/Tests/ForeFlightKMLTests/CoreElementTests/PolygonTests.swift
+++ b/Tests/ForeFlightKMLTests/CoreElementTests/PolygonTests.swift
@@ -97,4 +97,23 @@ final class PolygonTests: XCTestCase {
 
         XCTAssertFalse(kml.contains("<altitudeMode>"))
     }
+
+    func test_polygon_withInnerRings_producesInnerBoundary() {
+        let builder = ForeFlightKMLBuilder()
+        let outer = [
+            Coordinate(latitude: 0, longitude: 0),
+            Coordinate(latitude: 0, longitude: 1),
+            Coordinate(latitude: 1, longitude: 1)
+        ]
+        let hole = [
+            Coordinate(latitude: 0.2, longitude: 0.2),
+            Coordinate(latitude: 0.2, longitude: 0.8),
+            Coordinate(latitude: 0.8, longitude: 0.8)
+        ]
+
+        builder.addPolygon(name: "poly", outerRing: outer, innerRings: [hole])
+        let kml = builder.kmlString()
+        XCTAssertTrue(kml.contains("<innerBoundaryIs>"))
+        XCTAssertTrue(kml.contains("<outerBoundaryIs>"))
+    }
 }
diff --git a/Tests/ForeFlightKMLTests/TestHelpers.swift b/Tests/ForeFlightKMLTests/Utils/TestHelpers.swift
similarity index 100%
rename from Tests/ForeFlightKMLTests/TestHelpers.swift
rename to Tests/ForeFlightKMLTests/Utils/TestHelpers.swift
diff --git a/Tests/ForeFlightKMLTests/UserMapShapesSampleFullTest.swift b/Tests/UserMapShapeTests/UserMapShapesSampleFullTest.swift
similarity index 99%
rename from Tests/ForeFlightKMLTests/UserMapShapesSampleFullTest.swift
rename to Tests/UserMapShapeTests/UserMapShapesSampleFullTest.swift
index e350347..7d9f4ed 100644
--- a/Tests/ForeFlightKMLTests/UserMapShapesSampleFullTest.swift
+++ b/Tests/UserMapShapeTests/UserMapShapesSampleFullTest.swift
@@ -341,7 +341,7 @@ final class UserMapShapesRecreationTests: XCTestCase {
             )
         )
 
-        let kml = try builder.build()
+        let kml = builder.kmlString()
         let tempDir = FileManager.default.temporaryDirectory
         let fileURL = tempDir.appendingPathComponent("FFIconTest_Generated.kml")
 
diff --git a/Tests/ForeFlightKMLTests/UserMapShapesSampleIndividualTests.swift b/Tests/UserMapShapeTests/UserMapShapesSampleIndividualTests.swift
similarity index 100%
rename from Tests/ForeFlightKMLTests/UserMapShapesSampleIndividualTests.swift
rename to Tests/UserMapShapeTests/UserMapShapesSampleIndividualTests.swift