My dad put a metal roof on his house a few years ago. I believe he used this company:
Metal Roofing Systems in North Alabama
Anyways, you can see, each panel is about 18 inches wide and 10+ ft long. They were incredibly easy to install (my mom helped). They are held on by only 2 screws at the top and is a "floating" type of roof, which allows it to expand and contract as needed. I think the biggest draw back you will have is, your gutter system is going to get destroyed every winter. Once the snow starts melting, it slides off the metal roof, quick. Two years ago, my dad's gutters were flattened after the southern snow storm. I am sure they make better metal roofs to handle snow environments.