So whatever you put on the roof has to span 6 and a half feet? That's pretty far between supports for a roof.
I show you what I have and maybe you can get some ideas that will work for you.
I have a metal frame that was a green house for my run. It's in two different sections, and they don't...
Where do you live? Climate matters, and can change the advice. You can add your location to your profile, and then it's always there. For instance, if you get a lot of snow, you need to take that into account; the roof has to be able to support the weight.
How wide is the span between the metal...