If you have a listing with multiple structures that contain living areas, it is appropriate to display their combined square footage on your listing. You must also include a breakdown of the living area sqft per structure in the Public Remarks.
For example, the following property has two structures, each of which has finished, livable area:
In this instance, you would add the total living area of the first structure (3,749) to the second (704) to get a total above grade living area of 4,453 sqft. You must then enter a breakdown of each structure's living area in the Public Remarks section of the listing.