Here's a link to my DIY canopy. I had the intention of hanging it above the tank, but if you extended the sides down and made it the same size as the tank, you could do something similar that would sit on the tank
http://www.canreef.com/vbulletin/sho...t=41662&page=2
There are a lot of good canopies on here so I'm sure you will find something.