So the latest incarnation of my favorite family is living in one of the loft buildings, and there looks to be space for parking vehicles in the back. However, when I try to place a parking marker, it won't let me, saying that I "can't edit anything outside of the apartment" or whatever the message says. Have I overlooked another possible way to have personal vehicles (outside of moving into a house), or is my family doomed to walking, taxis and subways? :/

There's a thread here already on how to edit lots, but if you don't want to do that, you can:

Type in cheat move objects on
Put a parking space in your apartment.
Place car on parking space
Put car in sims inventory
Delete parking space
Type in cheat move objects off

Here's the thread:

http://www.modthesims.info/showthread.php?t=423229

Or, if using any of the default Apartments from Bridgeport, you can place down a car in any of the garages or parking spots already supplied.

If building your own apartment building then make sure you place the public space orb down in the room where the parking spots are if they are inside of a garage.

Um...how, exactly? This is kind of what I've been trying to do...
Also I'd rather not have to resort to cheats or hacks 'cos, knowing my luck, I'd mess up what seems to be an already fragile game code. >_>

Or you can just put a car in their inventory. Whathisface, Romeo Rake, the spy, lives in a high rise and has a shiny car in his inventory that he uses to get around.

Can you put stuff straight into their inventory, without placing it on the ground first?

AnnaIME:
With the moveobjects on cheat, you can place the car wherever you want, even in the bathroom. Go to live mode and place it in the inventory. That's all.

Maybe not relevent but I moved my sim into a penthouse and then suddenly she had a police car in her inventory. Really odd and funny.