Not a canopy DIY but the aluminum angle rails I used to mount my multi chip LEDs could easily be adapted to canopy use. I purchased the aluminum angle at Princess Auto as well. There are different thicknesses of material that affects the cost of the aluminum stock. I used very thin aluminum since each LED has it's own heatsink with fan.
Haven't quite finished the frame, but it's dong the job of lighting up the tank quite well.
If care to read more on the build, here's a link to the thread.
http://www.canreef.com/vbulletin/showthread.php?t=82206