GUI draw rectangle script not drawing rectangle!

I’m writing a 2D game on Unity’s GUI layer. I attached the Boo script below to the Main Camera and gave it a texture for boardBG, and it should just draw a rectangle. However it does not make any difference to the screen on the output if it is there or not - there is no rectangle. What am I doing wrong?

import UnityEngine

class genBoard (MonoBehaviour): 

	public boardBG as Texture
	public cellNumX as int = 10
	public cellNumY as int = 10
	public cellSize as int = 20
	public marginSize as int = 10
	private boardWidth as int = cellNumX * cellSize + 2 * marginSize
	private boardHeight as int = cellNumY * cellSize + 2 * marginSize
	def onGUI ():
		#Board background
		GUI.DrawTexture(Rect((-boardWidth / 2), (-boardHeight / 2), boardHeight, boardWidth), boardBG, ScaleMode.ScaleToFit, true)

Boo huh? Switch your language. Try C# or Javascript. Nobody really uses Boo. If you want help from other people, use one of those languages. Use javascript first if you are new to programming because it is an easy language. Once you have learned that, move onto C#. I don’t know any Boo so sorry to say that.