"Simmer_chiyen;c-17774895" wrote:
To do an open stairwell like you intended to do, you have to close up the space using walls or fences so that the game recognizes it as a “room”. Do not worry about blocking the stairway, the bit where the stairs attach should automatically clear out. Using your second image as an example, there actually should have a segment of invisible fence at the stairway.
As for the molding showing inside, there is very little you can do about that, unfortunately. It is just how Build Mode is designed—the game always designates an inside and an outside automatically for each room, and sometimes deleting floors makes the game deem the part as exterior.
This is how it's SUPPOSED to work; however, it's bugged right now, at least for me.