how can i make it so my blocks switch from grass to log because i have a switch script but i cant make the 2 blocks turn on and off for placing please help

using UnityEngine; using System.Collections;

public class WorldGenerator : MonoBehaviour { public GameObject grass; public GameObject log; public GameObject current;

 public float SizeX;
 public float SizeZ;
 public float SizeY;

 // Use this for initialization
 void Start()
 {
     StartCoroutine(SimpleGenerator());
 }

 void Update()
 {
 }

 public static void CloneAndPlace(Vector3 newPosition, GameObject originalGameobject)
 {
     GameObject current = (GameObject)Instantiate(originalGameobject, newPosition, Quaternion.identity);
     current.transform.position = newPosition;
     current.name = "Block";
 }

 IEnumerator SimpleGenerator()
 {
     uint numberOfInstances = 0;
     uint instancesPerFrame = 50;

             float height = Random.Range(0, SizeY);
             for (int y = 0; y <= height; y++)
             {
                 numberOfInstances++;

                 if (numberOfInstances == instancesPerFrame)
                 {
                     numberOfInstances = 0;
                     yield return new WaitForEndOfFrame();
                 }
             }
         }
     }