It's bad for wet environments and snowy ones. You need to be super vigilant about inspection and maintenance if you have a flat roof where I live in northern U.

It's bad for wet environments and snowy ones. You need to be super vigilant about inspection and maintenance if you have a flat roof where I live in northern U.S. While two feet of snow on the roof will provide a small amount of insulation, every material in contact with it needs to be rubberized or sealed every couple of years or both. Shovelling your roof with a flexible waterproof membrane can lead to gouges which defeat the impermeability. And one small leak can go unnoticed until it has seeped into the visible part of the house and rotted rafters and supporting timbers. Drainage on flat roofs get clogged and need to be cleaned or you end up with standing water. A sloped metal roof will last for 30+ years without any maintenance. A flat roof of any type will require several maintenance operations a year and last half that unless you have a commercial tar and gravel roof which is heavy and imposes additional load bearing requirements on the structure.