Hi alisaalthaus,
Welcome.
I'm no expert, but my build has 2X2 rafters on 24" centers with 1/4' plywood on top. I'll be using fiberglass tape over the seams and three coats of epoxy over everything. I can sit on the roof without hearing a creek, (before the tape and epoxy, that's next weekend), and I'm over 200 lbs.
From what I've read on other folks build albums, many use 1/8" on 1X2 stringers with aluminum over that. When you get a chance, use the search function at the top of your page, and go through some of the build albums. It's unbelievable how many, light weight, methods have been used with great success.
Best of luck on your build.
Brian