Alright, I remember being able to do this before in Sims 4, but for some reason, it isn't working now. Consider the following... This is the third floor in a three-floor sample building. The balcon...
Hm. I'll give that a try tomorrow, but if I'm not mistaken, that's exactly how I went about it. I staged everything using flat squares, outside, then moved them in. Maybe that step is doing something. I'll update you tomorrow. Did you test it to see if sims would go both up and down?