The house in Bloxburg that you own comes with only one floor by default, and you have the power to customize that one floor in any way you choose. However, if you spend 300 Robux for the unique Multiple Floors game pass, you will unlock the ability to construct up to five floors within the game. In addition, you can go ahead and purchase a basement game pass to construct a basement beneath the first level. That pass will cost you 100 Robux and, in my view, is a great option if you want to create multi-story houses in the game.