I am currently working on making a example layout using the scrapped Floor Builder Prototype, which will be planned to be part of the scrapped floor builder page soon. Here's a WIP look of it:
I also added the second floor using stairs! :)
I know he’ll update it, but it still stings that I can’t keep working on this layout anymore because of this. Also, this layout had a very high amount of objects that It took so long to load one level

It's kinda a bit strange that it's that high, considering the fact that the level is not very huge, It must've been because of the second floor or the amount of decorations I put in this layout. It’s also so bad that i'm losing performance of the game.
Besides, I think Floor Maker will fix the performance issues and stuff anyways. Floor Builder’s code is probably a bit outdated.
Yes you can and it has been a feature for like 2 years since they’ve worked on the floor builder. I was trying to add multi-height floor to this layout and it didn’t work out really well. If you really want to make a room tall or make multiple floors, press the up or down arrow, but do not add too much things when making a multi-height floors.