I think it would be neat if we could buy out the apartment next door to our Sims.
Ctrl+Shift+C
TestingCheatsEnabled true
Buydebug
RestrictBuildBuyInBuildings false
And then you can.
I also think it would be neat if we could pick the floor we moved in on
<technical detail>
There are two types of apartment buildings: Regular ones and "shell" ones.
Regular ones are built like regular homes, with some bits added to mark common areas, hide rooms and npc doors. There is at least one of these in bridgeport, can't recall the name.
Shell apartments are the skycrapper-esque ones, basically, you have a flat lot, on top you have a big tall huge object that is the building frame. The frame works very much like a column.. A huge, ridiculously tall, hollow and multi-floor column. You are still limited to the old number of floors as before (4~5 or so), because that's what the engine was designed for, it's just that deck 2 and on are now higher. Inside this hollow column apartments are built, much like a home, and non-player areas are marked much like non-shell apartments.
</technical detail>
Empty apartments are that, a big empty room with no objects inside, there isn't even a division between them, if there are several on a single floor, so letting the player pick & choose floor is just not that feasible under this system.
However, you can still use the above cheats and manually edit the building to have the apartment elsewhere, you can even do it in edit-town prior to playing.