You can cut steel roofing panels with a circular saw and a carbide blade, but it'll save you a lot of work if you order the panels the right length to start with. Plus, you'll have a greater color selection if you order the roofing rather than buy off-the-shelf panels. Remember to order in advance, though, since it usually takes several weeks for the roofing to arrive. And make sure the overhangs are the right size so the panels will overhang the fascia slightly.
