I've never seen a weight limit on any roof, of any brand of RV. Most just list "Walk On Roof", which I suppose you could take with a grain of salt. Every one I've walked on flexed quite a bit, but figure you're on 1/2" plywood at the most on a top of the line unit, or 3/8" or less on the entry level, each having rafters on 16" centers. The ladders are pretty flimsy and usually rated at 225 I think. If you're careful and walking mainly toward the edges and steering clear of any vent openings, I think you'd still be fine. I do like you, tread lightly.
John and Rebecca Dickson
Emma-7 / Little John-5 / Iva-1
Full Timing Again, Rev B
2013 Ford F-350 Lariat CC LB PSD
2015 SOB TT - With OC's Awning Poles (#8)
At least in Heaven, RVs will be perfect, and I won't have to keep fixing them.