Building a wall

I think the problem arises when you try to run Destroy(brick). Your prefab is assigned to brick in the Unity Inspector, which is simply a reference to the prefab in your local assets. The problem is, you are actually trying to "`Destroy()`" the local prefab in your Unity assets. Unity is just so nice and friendly, not letting you do that.

Instead, you should store the Instantiated gameobject into a GameObject variable, such as:

 var newBrick : GameObject = Instantiate(brick, Vector3(x,y,-4), Quaternion.identity);

If you wan't to destroy this brick in the future, you should use Destroy(newBrick).

i wrote a script to generate a brick wall that allows for configurable height, width, randomness of brick width, tapering in height and random material.

here is the script

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 
 
 public class BrickWall : MonoBehaviour {
 
     public AudioClip audioClip;
 
     public GameObject source_brick;
     public Material[] materials;
     public int n_high = 10;
     public int n_wide = 0;
     public float width = 100;
     public Vector3 brick_size = new Vector3(.7f, .5f, 5);   // this is the basic brick size, can me modified by brick_random_x_max and brick_top_row_z
     public float brick_random_x_max = 1.4f; 
     public float brick_top_row_z = .5f;
     public Vector2 gap;
     public bool bottomRowKinematic;
 
     // Use this for initialization
     void Start() {
 
         Time.timeScale = 1;
 
         Vector3 pos = Vector3.zero;
         Quaternion rotation = Quaternion.identity;
         // mother should i build a wall
 
         // pre calc widths
         for (int y = 0; y < n_high; y++, pos.y += brick_size.y+gap.y)
         {
             Vector3 localScale = brick_size;
             if (brick_top_row_z != 0) {
                 localScale.z = Mathf.Lerp(brick_size.z, brick_top_row_z, (float)y / n_high);
             }
 
             pos.x = 0;
             for (int x = 0 ; (n_wide==0) ? pos.x < width : x < n_wide ; x++)
             {
                 // build a row
                 if (brick_random_x_max != 0)
                 {
                     // randomize width
                     localScale.x = Random.Range(brick_size.x, brick_random_x_max);
                 }
 
                 Vector3 place_pos = transform.position + pos;
                 place_pos.x += localScale.x / 2;    // alling left size
 
                 GameObject brick = Instantiate(source_brick, place_pos, rotation, transform);
                 brick.transform.localScale = localScale;
                 Renderer rend = brick.GetComponent<Renderer>();
                 if (rend != null)
                 {
                     rend.material = materials[Random.Range(0, materials.Length-1)];
                 }
                 brick.name = "brick_" + x.ToString("D2") + "_" + y.ToString("D2");
                 pos.x += localScale.x + gap.y;
 
                 if(y==0)
                 {
                     if(bottomRowKinematic)
                     {
                         Rigidbody rb = brick.GetComponent<Rigidbody>();
                         if (rb != null)
                             rb.isKinematic = true;
                     }
                 }
             }
         }
     }
 }

to use it, create an empty object for your wall and attach this script. then create a cube (i guess any object will work) and make the scale 1,1,1. attach rigid body if you care about the physics. in the script, drag the cube to the source_brick slot drag your materials to the materials list (1 is ok) set the brick size if you set brick_random_x_max and public float brick_top_row_z to 0 it will be a standard brick wall brick_random_x_max gives you more of a stone wall effect brick_top_row_z lets you make a pyramid but in z direction only

i used this to make a dam wall

enjoy

PS, it doesn't scale or rotate. scaling you can take care of by changing the brick size parameter but it need rotation adding. maybe i'll add that when i have time