I'm not a welder (so to speak) but I have fabricated quite a bunch of goodies.
Let's think about some basics first.
Size = Figure the size based on the roof area where you'd like it. Keep in mind the measurements of the internal roof/support & cross braces. Calculate that area into the layout for final attachment. As close to you can get (outter edges of roof) where verticle sides meet the top.
Weight = I recommend 1/8" wall aluminum X 3/4" O.D.
Dimensions = Length X Width X 6" overall height. Round pipe will work fine, and easy to bend. I suggest the corners to be bent to 1/4 of an 8" radius.
Where the ends of pipe meet the sides of another, I recommend flattening them with a hammer, or notching them to match the radius of the length they meet with.
Schematic drawing coming soon
Copy/Paste this link into your browser for the bigger picture --->
http://img31.imageshack.us/img31/7176/draftj.jpg
