Stacking Lego pieces

Hey guys, Im making a weekend proejct. It will be a puzzle game, based on grid placing blocks. I can place them, but there is a slight problem with stacking. I need to check if the lego piece should or shouldnt go higher -- aka stack like a tower.

Lego.js

 var totalDist : float;
 var actualBlock : Transform;
 var blockIsPlaced : boolean = true;
 var block : Transform; //one lego piece
 var x : float = 0;
 var y : float = 0;
 
 function Update (){   
        CheckForPlacing();
        GetInput();
       
 
 if(!blockIsPlaced){
                actualBlock.position.x = x - 2.5 * totalDist;
                actualBlock.position.y = y - 1.5 * totalDist;}}
 
 function CheckForPlacing () {
  if(blockIsPlaced)
         {            
                actualBlock = Instantiate(block, Vector3(
                                          transform.position.x,
                                          transform.position.y,
                                          transform.position.z - 0.1
                                          ),transform.rotation);
                actualBlock.parent = transform;
                blockIsPlaced = false;}}
 
 function GetInput (){
         if(Input.GetKeyDown(KeyCode.RightArrow)){
                if(x != 5){
                        x += 1;}}  
     if(Input.GetKeyDown(KeyCode.LeftArrow)){
                if(x != 0){
                        x -= 1;}}
       if(Input.GetKeyDown(KeyCode.UpArrow)){
                if(y != 5){
                        y += 1;}}     
      if(Input.GetKeyDown(KeyCode.DownArrow)){
                if(y != 0){
                        y -= 1;}}
      
      if(Input.GetButtonDown("Jump")){
                blockIsPlaced = true;}}
     

• David

PS: I hope that you will understand. :-)