They're all completely open at the back and, like the stage set, there aren't any roofs apart from the lean-to type. If you add a wall add-on to the back of the arcade then you still have access from the front. I would add a wall add-on to either the front or the back of the open arcade, not both. I'll put up a post with photos of the upstairs rooms. And there are a couple of secret rooms for treasure and fugitives coming up!
Michael