I don't think you'll find any published figures for the weight capacity.
Don't know what exact model you have, but it should have a fiberglass roof covering, like my Lexi.
If your concern is if it's safe to get up top and walk around, then yes, it's ok. I'm up on our Lexi's roof almost monthly to do routine checks, and cleaning every other month.
Just don't get up there with flip flops. Wear a good pair of nonslip sneaks that have laces to tie. You don't want em comming off while up there...it can get slippery.
Steve & Cheryl + Zoey, and Ziggy, our furry kids.
2012 Forrest River Lexington 283ts
Toad, 2013 Subaru XV Crosstrek