Raycast textureCoord

Hello, I've been working with Unity3D for a couple of days now, and I'm stuck! I use the following code to create a platform using 1x1x1 cubes:

function Start() { for (var x : int = 0; x < 40; x++) { for (var y : int = 0; y < 40; y++) { count ++;

         block = Instantiate (BlockPrefab, Vector3(1.0 + (1.0 * x), 0.0, 1.0 + (1.0 * y)), Quaternion.identity) as Transform;

         block.name = "block_" + count;
         //Debug.Log(block.name);
     }
 }

}

This works just fine. Now what I want to achieve is being able to left click my mouse on a cube (I call them blocks in script) then create an other top right on top of the cube I clicked (my ultimate goal is being also able to click on a side of a cube and it will create a cube on that side), this is what I've got so far:

function Update () { if(Input.GetButtonDown("Fire1")) { var hit : RaycastHit;

     var ray : Ray = Camera.main.ScreenPointToRay (Input.mousePosition);

     if (Physics.Raycast (ray, hit))
     {
         var newPosition = Vector3(hit.point.x, hit.point.y+1, hit.point.z);

         block = Instantiate (BlockPrefab, newPosition, Quaternion.identity);
         count ++;
         block.name = "block_" + count;

         Debug.Log(hit.collider.gameObject.name);
         //Debug.Log(hit.textureCoord);
     }
 }

}

This creates the cube at any point in the map I click, except for empty spaces, I tried using Raycast textureCoord but it always creates the cube at 0,0,0. I found on answers.unity3d.com that I had to use a mesh collider for the cube and that's what I did but it still doesn't work.

What do I have to do to make it work?