Yes, you can 'walk' on the roof. I am about 270# and I do. However, I also place either 3/4" plywood or several wide boards on the roof, bridging the RIBS/rivets.
It is important that you also place some 'non-skid' material on roof before placing the board(s)...
Next, you climb up using a ladder, which is properly padded so it doesn't scratch...leaned against the curb or street side ZipDee awning.
Oh, make sure you have a "ground support" person to hand tools, parts, call 911 if you fall, of course the call would happen after the requisite YouTube video being posted successfully.
Peace and Blessings..