This guy demonstrates a pretty simple set of procedures for making steel-sheet roofing from 55-gallon steel drums. He uses the sheets he’s made for a roof on a shed addition to an existing building from reclaimed materials.
The roof-rafter arrangement and roof pitch in his project are more suited to rain country than snow country, though the sheet roofing could still be used in snow country.
I thought his use of the drum sheet metal was quite interesting. But I'll also mention the vid I’ve put embedded this post is one of a 7-Part how-to about building his 8’x8’ shed. He says he built the whole shed nearly free.