I created a replacement build for ThrifTea recently using primarily rounded walls and ran into so many issues, especially when using platforms and foundations.
I think one of the most frustrating things I found was an "Invalid Rounded Room" error. If you place a round room inside another room and delete the straight walls, the game gets big mad lol. It seems like free-standing rounded walls within another room really confuse the game and can prevent you from painting the interior/exterior of your build because the room become invalid.
Another issue I found is that when you place a rounded room inside another room and on top of a platform/foundation, the game may automatically generate a secondary diagonal wall that's attached to your current wall. This seems to originate from the platform/foundation below and really makes it difficult to place anything on the rounded wall. :neutral:
(I actually made a video about this on my youtube channel if anyone is interested lol. Link in signature)