The project area defined by the perimeter of a building plan is referred to as...

The footprint of a building is the area of ground that it covers, defined by its perimeter. It’s essentially the shape that results when you trace around the outer walls of a building plan. This term is used in architecture and urban planning to describe the space that a building occupies on a site. References: LEED Green Associate Candidate Handbook, U.S. Green Building Council resources