How do you make a second floor on the sim3 ds game video?

To create a second floor in The Sims 3 on the DS, start by selecting a house that has enough space. Use the build mode to choose the "Floor" tool and place a staircase where you want to access the second floor. Once the staircase is set, you can add flooring and walls to create the new level. Finally, furnish the second floor with rooms and decor as desired!