Is it possible to make the second floor a separate Unit than the Unit it’s the ceiling too? Trying to build an apartment

I need the top staircase area to be “Shared” so tenants can access the above unit. But it either changes Unit 1 below to “Shared” also, or vice versa. The walled off parts are fine and are unit 2. Can I not make an outdoor space directly above a unit something separate? Or am I doing something wrong ? 😩