ON my motor home, as I said the roof is more than strong enough The ladder, not nearly as strong (it is history, I use a much better ladder now)
The best advice I can give is be careful.. When I worked as a professional roofer we walked all over many roofs,, Some were good and solid Some not so much so you learned to set your foot down carefully "Feel" the roof and if it felt like it was going to let you down.. Step elsewhere, dig in the the straight claw hammer and inspect the rotted wood.. Replace it, build it up and continue the re-roof job.
If your roof feels "soft" or "Springy" or "Spongy" Be very very very careful
IF it feels like the kitchen floor.. that is how mine feels.