Story
Each level of a building is called a story (or floor). By default, all objects that are not parts of groups will be exported as one combined STL.
You can switch through stories via the hierarchy menu, by pressing ⇧ W and ⇧ S or by pressing the expand_more expand_less buttons on the bottom right of the screen.
If you move into a story that is higher than your current highest story, the Townbuilder will automatically expand your stories to fit.