This isn't a post about solar panel azimuth or anything so technical. It's far more practical advice I'm offering today: if you live in an area that gets a great deal of snow (currently we have between 2 and 3 feet), and you are going to be putting your panels up on your roof, make sure that you have a easy, safe method of clearing snow off of them. Yes the snow will eventually melt off, but I hate losing a full day of sun waiting. Clearing the snow off our panels is a chore that I do not enjoy, climbing the ladder onto the very slippery steel roof and clearing the panels is bad enough, but getting back off the roof and onto the ladder is NOT FUN. The only consolation is that if I fall it will be into four foot deep drifts and onto Gator, who will be trying to catch the falling snow, and will instead get me.
If I were doing it again I would build in a dedicated rest for the top of the ladder that prevented it from sliding sideways. Then I would build a metal catwalk with some angle irons and metal mesh - neither of which is an expensive material. For the sake of a couple of hundred bucks I'd be able to walk around the panels in confidence.
Better yet, if your site allows it, mount the panels on the ground.