My last game was Spelljammer snd they all just lived on the ship.
Before that, it was a magical school game and they lived in dorm rooms or grad student rooms most of the time. While on the road they stayed at inns or usually had some sort of magical abode to camp in. In cities, they used inns or stayed with important people as they were important people on school business doing important things. They did eventually move off campus to an abandoned inn they bought, restored, added some things to, and populated with all the NPCs they had adopted along the way*. Bastion rules didn't exist then, but probably would have worked.
ETA: In future games, besides bastions, it will probably be decided by Lifestyle costs and payments I will require and that will determine their housing. I'll also have mechanical benefits or penalties for the extremes, which will have some significant requirements on the high end when on the road as inns probably won't cut it.
ETAA: More to the OP, most housing are single units. The better lifestyle, the bigger and better they are. In rural areas such as village, they are typically of very sturdy stone construction, as they may have to act as panic room if some of the local megafauna wanders into town. In cities, it goes from tenements to apartments, and then multistory row houses with the business being on the lowest floor and housing above. Nobility and the really rich get mansions and castles. Wizard can get a tower, whose traditional shape goes back to when teleport could result in a higher or lower elevation, thus wizards usually teleport to the second or third story of their tower.
*In one case, they ran across a dwarven stone smith that had been fired by a noble. Only existed in the module to provide information, but they interacted with and adopted him and eventually hired him, gave him three years pay, a bunch of loot that he could also take money for equipment out of, and whole bunch of letters including one explaining to the other NPCs that he was there to build out the new additions to the inn that they wanted, and sent him off back to their home.