What do you mean by 2 floors? Unfortunately, you can't have two walkable areas above one another (horizontally) as the AI grid, the system that handles where you can walk or not, etc, is in 2D. If you want multiple stories, you'll have to make a separate terrain out to the sides of the existing one and use stairs / hatches / ladders as teleport from A to B. Open one of the inherited maps from Larian to see how they do it :]
