Normally, with that I just use extention poles, and do it from the ground. However I probable would do that with a ladder except I would have racked the ladder above the window. I dont know what you guys mean by the grid? and yeah used some leveling equipment for the ladders if needed.
Also it does look like there is a small walkway along the roof if you look at it, so I dont think he is standing on the slopped part of the roof.