Curved walls

Hey! Never noticed this before but just now trying to build something that is inspired by a real life building. The curved walls work nicely, like they are suppose to but only when u want the inside to be "inside the curve". Buuuuut if I want to build a room or a whole place "outside" the curve, it does not work and I can't figure it out. Is it suppose to be like that? Or do I just not realise how to work this game after playing it since 2014? xd Hopefully I explained it somehow understandably!