Rooms can only be added when you have the Lot open, following the steps below.

Click Place Household in the bottom right corner.Save the household or Sim to My Library.Click the Gallery button in the upper-right corner.Sims can be downloaded from the Gallery in two places: Create A Sim or Live Mode. Click on the Cloud icon in the bottom-left corner to upload your content to the Gallery.Open the Gallery, and go to the My Library tab.Save your household, lot, or room by clicking the Save button folder in the top-right corner.Click the download arrow button to save it to My Library.Find the Household, lot, or room you want to save.You can open the Gallery at any time by pressing F4, or clicking the Gallery button.

Create, share, and download content with players around the world. The Gallery is your opportunity to share your creativity with The Sims 4 community.