This happened to me! I was building on a fresh lot my sim had just bought and I couldn’t close the walls to make a building. Room tool worked fine. But I restarted the game after saving my progress and I haven’t had the error since.
I ran into the same issue. I found that not owing the building and assigning specific units ‘cleared’ things up. I was able to create an entire apartment building with separate units. You must create a unit and assign every room to that unit. (Bdrm - 23 Lazy Blvd, Apt 101; Bathroom - 23 Lazy Blvd, Apt 101). Any “shared” spaces are for all tenants. Until devs update and permit ownership while building without the ‘cannot build’ warning, that’s what I did.
