Hi, Bobozia.
It works the same as the PC version (though the controls are a little different). Remove the roof (if auto-roof is on, turn it off), then add floor tiles where you want the second floor to be. Make sure there are stairs leading to the upper floor. It's new to console players as the previous Sims games only allowed single floor houses.
Once you get more comfortable with the house design tools, you can start making some pretty impressive houses. Check out the Lodgy Lodge and Modern Zen houses for a couple of split level homes that looks pretty cool. And, of course, the Gothic and Mediterranean Villa houses are great mansion types.
I've recreated half of the houses from the PS3/Xbox 360 game in the PC version -- Lodgy Lodge, Blue Bungalow, Modern Zen and Adore Abode. I'm looking forward to doing the other four as well, though the mansion homes will likely be the hardest to do. I looked at the Garage-Mahal and that one looks like it would be pretty difficult. Quaint will probably be the easier to recreate. But, this is how I learn, heh.
Flynn
