Berezino's largest hospital (roughly in the middle of the city), northern room on the ground floor, it has several metal shelves.
If you approach the shelf on the north side of the room, the icon "climb up" pops up. If you select that action, you will find yourself outside, climbing the ladder that brings to the roof. (I suppose it's the ladder that stays just on the other side of the wall. In this case it's a clipping problem, related to issue #0000465.)