Or perhaps I just have very vague notions of the buildings I put my characters in. Since the precise locations aren't that important -- if I needed alibis and locked room mysteries I suppose it would be different -- as long as there ought to be space enough for all the rooms I need, I wing it. Most authors do, in my experience. Diane Wynne Jones's complaint about how the buildings are always bigger on the inside than the outside (except farmers' hovels) does not pan out in my reading.
Then, it's great fun to actually make it larger on the inside than on the outside -- non-Euclidean architecture, like non-Euclidean geometry, is more fun -- but it does mostly amount to having a character scowl over the way the spaces add up, or don't add up.
It can be a little awkward when trying to fill out the local color, especially in a crowded city where the signal detail is what the buildings around the character are and what they do on each floor.