When I built an extension of an overhang for tractors to add space for fire wood I matched the existing corrugated roofing.
When fall came around i was so afraid to dent the stuff I would lay a small chunk of plywood and then another.
This gave me a way to disperse my weight and not dent the roof so if you took a couple of strips of plywood up with you it might give you a little peace of mind.
Or just stay on the rafters...
Bill