tooltip to show from array C#

hello there fellow coders! im completely new to the whole unity and coding in general but i want to learn :) im atm building a little inventory, and i got it to put teh items into an array that i display via GUI buttons, my question is how do i make it so when i hover over the item in my inventory, that it read the "tooltip" string i got under my item.

this is my inventory script so far. thanks alot in advance!

 using UnityEngine;
 using System.Collections;
 
 public class inventory : MonoBehaviour {
  public GameObject[] itemSlots = new GameObject[10];
  public int i = 0;
 
  // Use this for initialization
  void Start () {
  
  }
  
  // Update is called once per frame
  void Update () {
  
  }
  
  void OnGUI () {
  GUILayout.BeginArea(new Rect(Screen.width-144, Screen.height-180, 200, 200));
  Rect r = new Rect(0,0,35,35); 
     for (i = 0; i < itemSlots.Length; i++){
  if (GUI.Button(r,itemSlots[i].GetComponentInChildren<item>().icon)){
  
  }
  r.x += 36;
    if(r.x > 108) {
       r.x = 0;
       r.y += 36;
    }
  }
  GUILayout.EndArea();
 }
 }

my item script if someone needs it is here:

 using UnityEngine; 
 using System.Collections;
 using UnityEngine;
 using System.Collections;
 
 public class item : MonoBehaviour {
  
     public bool isEquipped = false;
      public int itemId;
      public int buyPrice;
      public int sellPrice;
      public GameObject itemVisual;
      public Texture2D icon;
      public string tooltipText;
     
      // Use this for initialization
      void Start () {
      
      }
      
      // Update is called once per frame
      void Update () {
      
      
      }
      public void isEquippedCheck (){
      
      if (isEquipped == true){
      itemVisual.renderer.enabled = true;
      }
      else itemVisual.renderer.enabled = false;
      }
      
      
      
     }