depended on the size of the building that they "hit the edge" of.
one story (~ three inches) and we just placed them prone on the ground with no actions remaining. Just like the rules for landing on terrain with no landing area within three inches.
higher than one story, outta the game. If that's harsh, you can roll for falling damage, but given how hard PLF's can be and that five points of contact don't include a ten foot drop to pavement.... yeah just remove them from the game as a casualty.
Using Stalkers example, it's a common sense issue as to where you can place the landing template. Obviously, it's not gonna happen if you want to land on directly on a guy's back porch but the top of a warehouse shouldn't be too difficult. Generally, if you can fit the landing zone, template and at least two/three inch buffer, into a given relatively terrain free area, go for it.
-PFC joe