The Sims 2 and 3 Build Mode vs The Sims 4 Build Mode

I’m still trying To get used to building in TS4. I have a hard time building upper floors because I tend to create buildings by dragging the wall tool out one wall at a time and connecting them, not in “squares” or entire rooms at one. Yet it seems that tiles can’t be placed on upper levels when walls are connected to create a room, only when the rooms are created all walls at once. ?‍♂️