I’m really not sure exactly what you’re trying to do, but if you want a second floor without a first floor you can actually do that; just move up a level in build mode.
Might be easier to place a basic box room on the ground level first just to better see where your placement is, draw your second floor, and then delete the first floor.
I want the sims dev team to let us build a mini loft that doesn't require building an entire 2nd floor. (which means that the loft can be built with medium height wall and so) for my tiny living household in sims 4. Now the raising platform function isn't helpful at all because it wastes a lot of space with its bucky walls and foundation.
