C# How to have a toggle

Read the reference for GUILayout.Toggle: http://docs.unity3d.com/Documentation/ScriptReference/GUILayout.Toggle.html

You didn't specify what kind of rect. The example below displays a label in a rect if the toggle is ticked.

 private bool showRect = false;
 
 void OnGUI() {
     showRect = GUILayout.Toggle(showRect, "Show Rect");
     if (showRect) GUILayout.Label(new Rect(100,100,200,200), "My Rect");
 }