
All of it is a matter of obtaining and following good instructions. Of course, the more complex the roof shape, the more involved the installation will be. Metal roofs generally will take longer than standard shingles to install, because you must have good flashing, fitting, and details, rather than rely on sealants when installing a long term roof.
How easy is it to install metal roofing, compared to asphalt or other types of common roofs?