transform input field in editor window

How do I generate a transform input field in an editor window? This is just the helloworld example plus the input that I can’t get to work:

public class WallBuilder : EditorWindow
{
	
	string myString = "Hello World";
	
	 Object block;
	 int blocksWide;
	 int blocksTall;
	
	bool groupEnabled;
	bool myBool = true;
	float myFloat = 1.23f;
    
	// Add menu named "My Window" to the Window menu
	[MenuItem ("WallBuilder/WallBuilder")]
	static void Init ()
	{
		// Get existing open window or if none, make a new one:
		WallBuilder window = (WallBuilder)EditorWindow.GetWindow (typeof(WallBuilder));
	}
    
	void OnGUI ()
	{
		GUILayout.Label ("Base Settings", EditorStyles.boldLabel);
		myString = EditorGUILayout.TextField ("Text Field", myString);
        
		groupEnabled = EditorGUILayout.BeginToggleGroup ("Optional Settings", groupEnabled);
		myBool = EditorGUILayout.Toggle ("Toggle", myBool);
		myFloat = EditorGUILayout.Slider ("Slider", myFloat, -3, 3);
		EditorGUILayout.EndToggleGroup ();
		
		//block = EditorGUILayout.ObjectField(block, Object);
	}
}

block = EditorGUILayout.ObjectField(“Object”, block, typeof(Object));

Or if you want something else than object

public Transform root;
void OnGUI() {
	root = EditorGUILayout.ObjectField("root", root, typeof(Transform), true) as Transform;
}

http://docs.unity3d.com/Documentation/ScriptReference/EditorGUILayout.ObjectField.html