I'm thinking of it too. I've checked with a local place to me (Dublin, Ireland) which makes up covers for trucks (curtain siders, 40-foot artics etc), and for less than €100 he will do pretty much whatever I want up to 9 feet by 12 feet, ties, ropes, re-inforcement at edges etc. I'm now planning to visit a good tent shop to see if I can buy adjustable height poles. I'll check back in when I'm done.
I used 3/4" and 1" EMT (electrical conduit) for a canopy frame that I built for my race trailer. The tubing is 10' long but with a tubing bender and my welder I was able to make a very strong framework. Sorry I don't have any photos of it.
The same could be done using aluminum tubing and fittings that are sold at very good marine/boating stores.
I am going to use triple layer acrylic (like greenhouse panel) and surround it with aluminum channel, and have it slide under my roof rack. Fast, easy, and simple Except to build it. So, it will be 8' long 7' wide and likely be supported by swing out mini trusses (no legs or angled supports)