If your roof stays covered in snow it can cause damage if it gets too heavy. Bill Bach has an Instructables for build a snow ripper to help remove the snow from the roof in minutes.
He built it with a cutting side to cut frozen snow loose and then a scraping side to scrape the cut snow off. Ah just one of the joys of homesteading. This is pretty cool. Check out how to make your own snow ripper on Instructables. If you would rather buy a roof rake than make your own you can get one here.