My camper's roof is about 17' long, about 8' wide. That's 136 square feet, so one foot of snow on that would be 136 cubic feet. A cubic foot of snow is something like 15lb/cubic foot.
15 pcf x 136 cf = 2,040 very evenly-distributed pounds.
I don't know about rating roofs in terms of people, but I'm going to try and sweep literally a ton of snow off my roof. I'm more concerned about the snow retaining a bunch of melt-water around all the roof penetrations when it warms up. Then there's the freeze-thaw cycles...
Not worth going out in the middle of the night, but still...