Within reason, and if you can avoid shadows, a ground mount is better than a roof mount – especially in snow country. If you do live in snow country, be sure you build the mount high enough to allow for snow accumulation below the panels. But low enough to let you clean the panels with a long-handled squeegee.
Almost all the early panels in my neighborhood, including my original pair, were mounted on roofs for what seemed at the time excellent reasons. They’re out of the way, shadow-free, and – I dunno – closer to heaven or something. It just seems like the instinctive thing to do. But at 65 years old I’m the youngest full-timer in my neighborhood, and working a long-handled squeegee while balancing on an ice-covered aluminum ladder on a frigid morning is a good way to not get any older. I usually just clean my lower panels and leave the roof-mounted ones for the sun. But my neighbors don’t have the luxury of that flexibility.
Just think twice about roof mounts, is all I’m saying. They might be necessary in your area due to space restrictions or shadows, or maybe you don’t have to worry about snow. Fine, but you’ll still have to clean them from time to time.