MegaMek

>- Is the skidding rule an exception to the "cannot
>move onto the top" rule?

I am going to go with "can 'o worms." It *looks* like it is an exception that may be "subject to change by executive interpretation." GenCon is this week. How about waiting on any changes until late next week?

>- If so, and a Tank ends up on top of a Building, is
>it stuck there until the Building collapses (at which
>point they take falling damage like falling into a
basement)?

There is no rule restricting a vehicle from moving *off* a roof (well, inherent restriction). Movement restrictions are typically related to moving *into* hexes not to moving *out of* hexes.