Practically when installing a metal roof, you need to use a drill with at least 3 different bits dimension as you would use metal roof screws and nails for the roof to be mounted on the roofs framework. A hammer will do the purpose for these screws and nails.
The problem with metal roofs is that 1) they attact lightening and 2) they don't keep heat in as well as a wooden or vinyl roof. You can try attaching sheets of tin or anodized aluminum to your existing roof. I would make sure that you have a lightening rod though.
