Guess it depends on the model. The Cherokee slide roofs are walkable. The only way to get to the seals is by being on the roof. I weigh more tan 200, not going to say HOW much more, but lets just say there is a zero involved at the end. I needed to caulk a seal above the street rear slide, and it supported my weight just fine, didn't even flex. I asked when I did the walkthrough if the slide roofs can support walking and they said up to 250 pounds.
OK for the naysayers, bunkhouse beds? have you seen them? They support 300 pounds, are you seriously going to say that the roof is flimsier than the bunk beds? On my long slide there is a cabinet floor to ceiling taking up half the slide. The other slide has a cabinet at one end for the reefer, and that is the one I was on to caulk the seam.
You don't want to tap dance on them or play bouncy house, but from what I have looked at, they are walkable. Just use common sense and be careful on them.