Use of space above garage

After having read in several places that it is apparently difficult to officially use the room above the garage as, for example, a study or guest room, I wanted to put a different idea on the table:

Is it possible to use the room if I maintain a 3m distance from the neighbor and do not construct the garage as an adjacent building on the boundary?

What needs to be considered here?

You definitely need a building permit for an extension on the garage. I don’t know which federal state you come from, the requirements vary from state to state, so unfortunately I can’t tell you anything more specific.

I come from Bavaria.