Unity How to create buildings on mouse click

In this example two buttons are created. On a mouse click the prefab is created.

GUIManager.cs

using UnityEngine;
using System.Collections;
 
public class GUIManager : MonoBehaviour {
	private string building;
 
	/* TODO: Check if clicked on existing object */
 
	void Update () {
		// left mouse clicked but not on GUI
		if (Input.GetMouseButtonDown(0) && GUIUtility.hotControl == 0)	{
			Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
 
			switch (building) {
				case "Base":
					Instantiate(Resources.Load("Base"), ray.GetPoint(10), Quaternion.identity);
					break;
 
				case "Barracks":
					Instantiate(Resources.Load("Barracks"), ray.GetPoint(10), Quaternion.identity);
					break;
 
				default:
					break; // build nothing
			}
		}
	}
 
	void OnGUI () {
		if (GUI.Button (new Rect (10, 10, 150, 50), "Build a HQ") ) {
			building = "Base";
		}
 
		if (GUI.Button (new Rect (160, 10, 150, 50), "Build a Barracks") ) {
			building = "Barracks";
		}
	}
}