tooltip on GUI layout ?

Hi All I am using GUILayout. But my problem is that I want to implament a tooltip into every button created how would I do that ?

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 //============================================================================
 // TowerManager
 //----------------------------------------------------------------------------
 // 
 //============================================================================
 public class TowerManager : MonoBehaviour
 {
     //----------------------------------
     // Public
     //----------------------------------
     public List<Tower> towers;
 
     //----------------------------------
     // Private
     //----------------------------------
     private int? activeButton = null;
     private GUILayoutOption[] button = {GUILayout.Height(30), GUILayout.Width(30) };
 
     //----------------------------------
     // SelectedTower
     //----------------------------------
     public Tower selected
     {
         get
         {
             if( activeButton.HasValue )
             {
                 return towers[(int)activeButton];
             }
 
             return null;
         }
     }
 
     //----------------------------------
     // Ghost
     //----------------------------------
     public Tower ghost;
 
     //----------------------------------
     // AWAKE
     //----------------------------------
     void Awake()
     {
     }
 
     //----------------------------------
     // ONGUI
     //----------------------------------
     void OnGUI()
     {
         GUILayout.BeginArea( new Rect( Screen.width - 50, 25, 50, Screen.height ) );
         GUILayout.BeginVertical();
 
         foreach( Tower tower in towers )
         {
             if( activeButton != towers.IndexOf(tower) &&
                 GUILayout.Button(tower.icon, button ) )
             {
                 Griddy.Terrain.Clear();
                 activeButton = towers.IndexOf(tower);
                 Griddy.Cursor.state = CursorState.PlaceBuilding;
                 SetGhost( selected );
             }
             else if( activeButton == towers.IndexOf(tower) )
             {
                 float a = Mathf.PingPong( Time.time, 1 );
                 GUI.color = new Color( 1, 1, 1, a );
                 GUILayout.Label(tower.icon, button );
                 GUI.color = Color.white;
             }
         }
 
         GUILayout.FlexibleSpace();
         GUILayout.EndVertical();
         GUILayout.EndArea();
     }
 
     // UPDATE
     void Update()
     {
         if( Input.GetKeyDown( KeyCode.Space ) )
         {
             Clear();
             Griddy.Cursor.Clear();
         }
         if( ghost != null)
         {
             if( Griddy.Grid.activeMarker != null)
             {
                 ghost.SetPosition( Griddy.Grid.activeMarker.position.x, Griddy.Grid.activeMarker.position.y );
             }
             else
             {
                 ghost.SetPosition( -100, -100 );
             }
         }
     }
     
     void SetGhost( Tower _ghost )
     {
         if( ghost != null )
             Destroy(ghost.gameObject);
     
         ghost = (Instantiate( _ghost.gameObject ) as GameObject).GetComponent<Tower>();
     
         foreach( Material material in ghost.renderer.materials )
         {
             material.shader = Shader.Find("Transparent/Diffuse");
             material.color = new Color( material.color.r, material.color.g, material.color.b, 0.7f );
         }
     }
     
     public void Clear()
     {
         activeButton = null;
         Destroy( ghost );
     }
 }    

Could someone please format my code because my internet is down and I am using my blackberry and cannot do it myself ? :(