An interesting question that I would be curious about as well.
I can lift up the roof on my Palomino SS1500 or at least lift it up to where it has slop in the lifting mechanism by getting under it in the partially raised position and lifting up on it by pushing up with my arms in the center. I did it to see how much play there was in the RT lift system, not much, maybe 1/2" of play.
I don't have roof ac, solar or a rack on top, I do have an awning though. My rough estimate of mine is under 200 pounds. Don't think I can lift much more and I was grunting a bit...lol
My manual states maximum allowable carry weight on the roof is 150 pounds but I think that has more to do with the capability of the RT lift system than the structural capability of the roof.
I'll be following along, I'm curious myself now that you posted it.