Generally-speaking, you just pick a house for your character to "stumble upon;" the city as a whole is in various states of abandonment, which makes it fairly convenient for the players to let their character find a place that's pre-furnished more or less to their liking(or entirely not to their liking, if you think that's funnier!). The buildings that have multiple people living in them are arrangements that all the players involved have made between themselves.

You don't need to pick a place for your character to live out of what's shown on the map, but it does tend to help for references' sake! And of course, if you'd like to have him perhaps "discover" a new shop or something along those lines where he might choose to take up residence instead of a house/apartment, feel free to talk it over with any of the mods and we'll be happy to help work something out!