My little hoop coop is roofed over with corrugated metal roofing. The hoop is actually a 8 x 5 base frame with electrical conduit hooped as ribs on the ends and in the middle. I put hardware cloth up the sides 18" and then drilled holes and attached it to the roofing. If you use cattle panels, I think attaching everything would be easier. We used the conduit because it was cheaper.
To answer your question, I think metal roofing would be great. It does add weight, and I think many people are intimidated by the thought of cutting and drilling metal. A tarp is easier to manage. My husband handles all the metal work around here. Otherwise, if I was doing it myself, my hoop house would have a tarp too! :)