The building itself is tall and grey. There is always a party in the room next to Tom's (complete with music and flashing lights). The inside of Tom's apartment is only shown once briefly in Zombeh Attack 3, it has grey walls and has a living room, kitchen, bedroom and (most likely, but never shown) a bathroom. In this episode, it's also seen that his apartment's number is 27.
Reason for Leaving
It was explained through a conversation in WTFuture that, after Tom shot Tord's skeleton in Zombeh Attack 3, he never bothered to clean it up. His landlord figured that the skeleton was Tom's, assumed he was dead and rented the room out to someone else.