private Rect windowRect = new Rect ((Screen.width - 200)/2, (Screen.height - 200)/2, 250, 150);
    public bool active= false;

    void OnGUI ()
    {
  if(active)
   windowRect = GUI.Window (0, windowRect, DialogWindow, "Test");
    }
    void DialogWindow (int windowID)
    {
  if (GUI.Button (new Rect (5, 30, windowRect.width - 10, 25), "Test01")) {
   Debug.Log("Test01");
  }
  if (GUI.Button (new Rect (5, 60, windowRect.width - 10, 25), "Test02")) {
   Debug.Log("Test01");
  }
    }
    void OnTriggerEnter(Collider other)
    {
  if (col.other == "Player")
  {
   Player.GetComponent<CharacterController> ().enabled = false;
   active = true;
  }
    }
    void OnTriggerExit(Collider other)
    {
  if (col.other == "Player")
  {
   active = false;
  }
    }
}

void isActive()
{active = !active}