They can carry significant load in theory, but like everything else the implementation details matter. Mine has been calculated to handle ~100 lbs/square foot. Partly this is due to my choice of heavy duty straps on the hub connections. On a home that needed to be able to be able to handle heavy loads I would go with a structural panel construction rather than a hub-strut frame. There is more than one way to do it, of course.
I imagine the greater concern is the flat top which won't actively shed snow, and the impact of this constant moisture on the roofing. Many domes are tightly sealed, often with exotic materials, for this reason. I love the snow here; it's just more insulation.
I haven't seen the domes in Wisconsin, but I dream of building some large botanic domes here some day. First I need some land, which gets more expensive here every year.
Susan, I don't know about your gardens, but covering all of mine is going to take some major engineering. I'll need all the labor I can get!
