I can't add fencing around them either.
Unfortunately I'm just finding them completely frustrating and impossible to use. I don't know if it's easier on PC but they can't be used for anything. I have to delete them but even then they leave a ghost outline and that space will be bugged unless I delete the entire floor and start again.
I tried to build a lighthouse and I wanted railings around the tower but I couldn't, even by using a round deck, then adding a round room. It won't let me do that. I couldn't get an image of the error messages as they just flickered for a split second.
At the top of the tower I wanted a roof, but the round roof was the wrong shape for the round room and it looked like it was floating. Even thick roof trims didn't help.
I just had to scrap the rooms but because the controls on consoles (I'm on Xbox Series S) broke with patch 1.69 I can't always delete a room. I have to try and take a sledgehammer to it but that caused more problems and increases the likelihood of the ghost round walls being left behind.
I'm just not using them again, unfortunately they are not functional and add hours to building time.