Idea like idea is okay if you ask me. Although there are some concerns of course. This appartment has to be in someones possession, someone has to have ownership over it in the legal world and cuz you want everything to be legal. You could however go further and tokenize this apartment or even many more apartments in future and thus every owner of the token has some ownership over the apartments. This is easy to implement but hard in practice as you already know we would have to trust the guy (you or somebody else) who has the right ownership of that apartment. As I am not sure if anything could be done on the legal side to have multiple owners. Because now everything should work right as long as the guy who owns apartment is honest, which is why it could be a bit hard to pull off if you ask me.
The apartment should be owned by a Legal Entity - like a trust and not by an individual. Gathering trust of potential investors is challenging, but so is the case with any legitimate business. It's easy to pull off a scam when you promise multi digit returns monthly.
This will probably need a tie up with a trust worthy entity - I don't know.