I often use two floors in my games. For this I just set up two divided maps and determine a few tiles (pred.tiles for example) as stairways, connecting the two floors. Mostly I set up then an elevator and a few "vertical" air vents, too. Latter one only can be used by the aliens (but not by the big ones, like Royal Guard or Queen).
So I've finally got in a couple games (loving it). But my friends and I were thinking about adding multiple levels. I was wondering if anyone else is already house ruling this.
Some of our thoughts were that the aliens could destroy floors using multiple actions, and could go up and down, same with predators, but humans could only go down. Also that the human scanners wouldn't tell what floor, like in aliens... so that would be more tricky to play... or have tokens on all floors until LOS... You know, things like that.
I'd love if others are already doing this, and how it's playing.