Actually, using the dungeon mechanic would totally defeat the purpose of adding extra floors for most people - you wouldn't see the building soaring into the sky,just a single level floating in space
The Devs are working on this, and they've already said they wanted to implement it for a long time, but it probably won't be anytime soon unfortunately
You could always make a "reverse skyscraper" or "groundscraper" - build down into the dungeons under your buildings, just be sure to build nice solid walls to keep out the nasties in the dungeon
What's that you're eating? A nice, juicy apple? You weren't supposed to eat that you fool, you were supposed to make it into a pie! - last words recorded words of Francis D'Avre before he went looking for snowcherries, but found a hungry Yeti instead.