Script is working incorrectly. (rotation)

I have a simple script, that places copies of a prefab object on the scene at a certain order.

To the prefab is attached the following script:

 var x:float = 0.0;
 var y:float = 90.0;
 
 function Start ()
 {
 var z:int;
 z=Random.Range(1.0, 4.0);  
 x=(y*z);  
 transform.Rotate(0.0, x, 0.0);
 print(x);
 }
 
 function Update () 
 {
 }

This script is supposed to turn the object by 90 degrees on y axis up to four times on start, in order to randomize the placement, but keeping the structure.

Problem is, when I launch the placement script, those prefabs that are turned are placed out of their place in structure.

Prefab consists of a three cubes, that are combined in an empty object.

Here is a placement script, just in case. It works fine by itself. It creates a grid of prefabs, placed in a square with a changeable distance between them and the size of a square itself.

 var Xvalue:float = 0.0;
 var Zvalue:float = 0.0;
 var ChangeCounter:int = 1.0;
 var ChangeAmount:float = 20.0;
 var Technical_Couter:int = 1.0;
 var PlayFieldSize:float = 0.0;
 var prefab1:Transform;
 var a:float=1.0;
 var b:float=1.0;
 

 function Update () 
 {
     if(ChangeCounter<PlayFieldSize)
         {
         Xvalue=(ChangeAmount*ChangeCounter);
         Instantiate (prefab1, Vector3(Xvalue, 0.0, 0.0), Quaternion.identity);
         print("Starting a new circle, placing first platform");
 
         //On the first circle x=0
         
     if(ChangeCounter>0)
     {
         while(Technical_Couter<(ChangeCounter+1))
             {
             Zvalue=(ChangeAmount*Technical_Couter);
             Instantiate (prefab1, Vector3(Xvalue, 0.0, Zvalue), Quaternion.identity);
             print("vertical row");
             print(a);
             a++;
             Technical_Couter++;
             }
         
         while(Xvalue>0)
         {
             Xvalue=(Xvalue-ChangeAmount);
             Instantiate (prefab1, Vector3(Xvalue, 0.0, Zvalue), Quaternion.identity);
             print("horizontal row");
             print(b);
             b++;
             
         }
     }
         
         a=1.0;
         b=1.0;
         ChangeCounter++;
         Technical_Couter=1.0;
         }
 }