Re: Sims 4- won't let me paint walls
@trillarie I've merged your new post with your existing thread. Sorry that no one got back to you before now.
I'm not an expert builder, or anything close, but have you made sure the affected room is actually an enclosed room? If it is, you should be able to click on it and see the entire room outlined in yellow. If it's not, you can try tracing over the walls, one at a time if you want, until the game reads it as a room.
Please also let me know what draw distance is set to in the game options. If it's low, turn it to high and see whether that makes a difference.