Lunar Dome Question

Friends,

Numerous authors have proposed building lunar colonies by building
domes over craters.

How large could such domes be? I imagine it would not be too hard to
build domes a couple of kilometers across, especially in the lunar
gravity, but could we actually dome over craters fifty or a hundred
kilometers across (and several kilometers high)? Any engineers out
there want to tackle this one?

Also, what about domes on smaller bodies, like one of the moons of
Saturn? I imagine that since these moons are mostly ice, one would
have to build insulated floors so the ice would not melt (I imagine
that if the ice melts it would shift the foundation enough that it
could possibly crack the dome...uh oh!). And any tunnels built into
the ice would also have to be insulated (I imagine this would be less
of a problem on the moon or Mars). On the other hand, the gravity on
these moons is so low that one could probably build larger domes.

Any thoughts on this?

Thanks.

Mark