Not sure why you are so worried about roof damage. Installed correctly, panel hardware will pentrate the roof, but so do shingle nails and lots of other things. My installer caulked EVERY screw that went into the roof and we have had no problems (I check often). I have panels on a 2nd story roof and on the single story garage roof. Don't have pictures now, but will try and get some.

If you have the room, then on-ground panel racks are great. You can position them for best sun exposure, there is no working on a roof (damage or not, that can get scary), often you can plumb easier and there is less dynamic head when filling the panels. But, they can take a LOT of room (depending on how many you install) and they ain't the prettiest lawn ornaments!