Multilevel floors

How do you make multi level floors in the sims 3? I want to make "plateaus" on the first floor, but if i just use flooring without a foundation for the lower parts and a foundation for the higher parts the walls do not attach properly to each other. Problems i suspect is that the heads of the sims will stick out of the floor of the floor above, so these floors need to be placed higher. I understand there needs to be some "cheating" in the command prompt but what is the easiest way of creating multi level floors? And are there any known bugs related to building houses like this?