TowerPlacement.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.InputSystem;

public class TowerPlacement : MonoBehaviour
{
    public LayerMask tileLayerMask;
    public float towerPlaceYOffset = 0.1f;
    public PreviewTower previewTower;

    private TowerData towerToPlaceDown;
    private bool placingTower;
    private TowerTile curSelectedTile;
    

    private Camera cam;

    void Awake (){
        cam = Camera.main;
    }

    public void SelectTowerToPlace (TowerData tower){
        towerToPlaceDown = tower; 
        placingTower = true; 

        previewTower.gameObject.SetActive(true);
        previewTower.SetTower(tower);
    }

    void Update (){
        if(placingTower){
            //shoots a ray from the mouse cursor to wherever 
            Ray ray = cam.ScreenPointToRay(Mouse.current.position.ReadValue());
            RaycastHit hit; 

            if (Physics.Raycast(ray, out hit, 99, tileLayerMask)){
                curSelectedTile = hit.collider.GetComponent<TowerTile>();
                previewTower.transform.position = curSelectedTile.transform.position + new Vector3(0, towerPlaceYOffset, 0);
            }else {
                curSelectedTile = null;
                previewTower.transform.position = new Vector3(0, 999, 0);
            }

            if (Mouse.current.leftButton.isPressed && curSelectedTile != null && curSelectedTile.tower == null){
                PlaceTower();
            }

            if (Mouse.current.rightButton.isPressed){
                CancelPlacement();
            }
        }
    }

    void PlaceTower (){
        Vector3 pos = curSelectedTile.transform.position + new Vector3(0, towerPlaceYOffset, 0);
        GameObject tower = Instantiate(towerToPlaceDown.spawnPrefab, pos, Quaternion.identity);

        curSelectedTile.tower = tower.GetComponent<Tower>();

        GameManager.instance.TakeMoney(towerToPlaceDown.cost);

        CancelPlacement();
    }

    void CancelPlacement (){
        towerToPlaceDown = null;
        placingTower = false;
        curSelectedTile = null;
        previewTower.gameObject.SetActive(false);
    }
}