ArcGIS (even ArcScence and ArcGlobe Explorer), like most GISystems, don't really have the capability to represent data in three dimensions. The closest they come is what's referred to as "2.5D" - and x, y and some value at that location, like elevation.
That said, you really aren't dealing with information that's truly 3D. Humans are stuck to the Earth, so we can't really move in 3D. Our buildings reflect that fact. And that can be modeled in GIS.
Start with a layer that provides footprints for your complex of buildings (in case you want to route between buildings). Then use a series of layers for each building - each one representing a floor in the building. You can even set topology rules for things like stairwells and hallways.
For routing, you'll want to create a network of paths (hallway center-lines). These center-lines will have special endpoints at stairwells, elevators and entrances. Then you either route on a single floor or route to an exit from the floor. Most floor exists (stairwells and elevators) provide access to all other floors. Makes it a little easier.