Metal roofs have become the standard in rural Alaska. Durable, attractive, low maintenance, easily installed, good in wind, fire resistant and great for sliding snow, metal roofs come in several different profiles and many colors. We primarily use the 29 gauge Norclad profile with #14 screws and 15# felt underlayment. We always sheath our roofs with plywood or OSB instead of using purlins.
The roofs are called lifetime roofs and will indeed outlast most of us. There are many of the old tin roofs put on in the thirty's and forties that are still functional.
From a remote builder's standpoint, a properly installed metal roof rarely prompts a warranty call. I have even seen improperly installed roofs perform well.
He who knows all the answers has not yet been asked all the questions. - Author unknown