Adding Imperfections?

Hey guys,

Sorry for the non-descriptive title, but I couldn't think of what to call this. What I have here is a home-made code to make a large cube out of smaller cubes. What I want to do is have it load the cube, but with random "gaps", or missing cubes. Similar to THIS, but without the red and blue stuff... Following is the code I wrote that "loads" the cubes. If anyone can give me some advice, or give me a start, I will be grateful!

 using UnityEngine;
 using System.Collections;
 //Written By Gibson Bethke ][ GBStudios
 public class LoadQuadrateCode : MonoBehaviour {
     public GameObject blockPrefab;
     public int blockSize = 3;
     public int rowSize = 7;
     public float loadingSpeed = 0.05F;
     public bool doneLoading = false;
     
     int iUp;
     int iToTheRight;
     int iBack;
     int upRowSize;
     int actualRowSize;
     
     Vector3 initialPosition;
         
     void Start () {
         actualRowSize = rowSize -1;
         initialPosition = gameObject.transform.position;
         InvokeRepeating("Load", 1, loadingSpeed);
     }
     
     void Load () {
         if(iUp == rowSize && iToTheRight == actualRowSize && iBack == actualRowSize) {
             doneLoading = true;
             CancelInvoke();
         }
         if(iUp == rowSize && iToTheRight < actualRowSize){
                 iUp = 0;
                 iToTheRight ++;
         }
         if(iUp == rowSize && iToTheRight == actualRowSize && iBack < actualRowSize) {
             iBack ++;
             iUp = 0;
             iToTheRight = 0;
         }
         if(iUp < rowSize) {
         Instantiate(blockPrefab, initialPosition + new Vector3(iToTheRight * blockSize, iUp * blockSize, iBack * blockSize), Quaternion.identity);
             iUp ++;
         }
     }
 }

Thanks for your attention, and help guys!

-Gibson

-Edit:

I have implemented Random.Value like Warwick Allison said, and it is working fairly well; is it possible to make it more predictable? The following is my update code.

 using UnityEngine;
 using System.Collections;
 //Written By Gibson Bethke ][ GBStudios
 public class LoadRandomQuadrateCode : MonoBehaviour {
     public GameObject blockPrefab;
     public int blockSize = 3;
     public int rowSize = 7;
     public float loadingSpeed = 0.05F;
     public bool doneLoading = false;
     public float amountOfRandom = 0.5F;
     
     int iUp;
     int iToTheRight;
     int iBack;
     int upRowSize;
     int actualRowSize;
     
     float randomNumber;
     
     Vector3 initialPosition;
 
     void Start () {
         actualRowSize = rowSize -1;
         initialPosition = gameObject.transform.position;
         InvokeRepeating("Load", 1, loadingSpeed);
     }
     
     void Load () {
         randomNumber = Random.value;
         if(iUp == rowSize && iToTheRight == actualRowSize && iBack == actualRowSize) {
             doneLoading = true;
             CancelInvoke();
         }
         if(iUp == rowSize && iToTheRight < actualRowSize){
                 iUp = 0;
                 iToTheRight ++;
         }
         if(iUp == rowSize && iToTheRight == actualRowSize && iBack < actualRowSize) {
             iBack ++;
             iUp = 0;
             iToTheRight = 0;
         }
         if(iUp < rowSize) {
             iUp ++;
             if(randomNumber < amountOfRandom) {
                 Instantiate(blockPrefab, initialPosition + new Vector3(iToTheRight * blockSize, iUp * blockSize, iBack * blockSize), Quaternion.identity);
             }
         }
     }
 }

Again, thanks for the help, guys!

-Gibson