In our case, the metal roof was hand built by my father-in-law for his granddaughter
out of some aluminum sheet roofing that was literally lying around (our property came with a lot of spare parts), leftover fencing, and some metal pipe and some metal conduit. It's a pretty simple design. I'd be happy to take more pictures for anyone needing a better look at construction details.
If you just do a simple shed roof rather than a peaked roof, it's even simpler to build. There are many suppliers who make simple metal roof structures or kits meant for use in horse or other livestock shelters.

If you just do a simple shed roof rather than a peaked roof, it's even simpler to build. There are many suppliers who make simple metal roof structures or kits meant for use in horse or other livestock shelters.