Is there any way to represent floors in a building using GIS?
(Also, it's stupid that I have to use existing tags cos none suit my question so I had to choose one at random.)
If you just need 2D symbology, simply add an integer numeric field and enter the number of floors in it. You can either use symbology and/or labels to indicate the floor number. If you have access to the 3D analyst, the previous procedure can also be used, but I would use height instead. In this way, you can extrude the building height above a surface getting a fairly useful representation of buildings (sans roof) in a landscape if draped over a DEM.
Some applications will utilize a different map services for each floor, since you often will see enough differences that just toggling a couple layers on or off don't cover what you are looking for.
Sometimes you can store each floor in the same MXD (assuming ESRI is your platoform) and set a bookmark to each area, then you just jump between bookmarks to view the different floor.
So depending on what your user experience is will dictate what direction you want to go; I have done web-apps based on ESRI software that we use different services or layers to switch between the different views. If you are in a desktop/thick-client mode; you can easily switch between different files one for each floor.