PlatformController.cs

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

public class PlatformController : MonoBehaviour
{
    // Start is called before the first frame update
    private bool showMenu = false;
    public GameObject tower;
    public GameObject prefabTower;


    void Start()
    {

    }

    // Update is called once per frame
    void Update()
    {

    }

    void OnMouseDown()
    {
        showMenu = true;
        Debug.Log("Click");
    }

    void OnGUI()
    {
        if(showMenu && !tower)
        {
            Vector3 pos = new Vector3(transform.position.x, transform.position.y, transform.position.z);
            Vector3 crd = Camera.main.WorldToScreenPoint(pos);
            crd.y = Screen.height - crd.y;

            GUI.Box(new Rect(crd.x - 150, crd.y - 100, 310, 200), $"Управление башней {gameObject.name}");
            if (GUI.Button(new Rect(crd.x - 145, crd.y - 70, 290, 30), "Купить башню"))
            {
                showMenu = false;
                //prefabTower = Resources.Load("Prefabs/Tower", typeof(GameObject));
                //GameObject instance = Instantiate(Resources.Load("Tower", typeof(GameObject))) as GameObject;
                tower = Instantiate(prefabTower, gameObject.transform.position, Quaternion.identity);
            }
            if (GUI.Button(new Rect(crd.x - 145, crd.y + 70, 290, 20), "Закрыть меню"))
            {
                showMenu = false;
            }
        }

    }
}