Building footprint

I am working on the office project and have a little hard time determining building footprint. The ground floor is mainly lobbies and some minor retail, but, there is also a road around the building, that is enclosed under building arcades, below 1st floor and ended with external wall . Basically it looks a little like tunel around potion of the building, leading to underground garages. It looks to me that it should be included in building footprint, as it is within external facade of the building and under arcades, but would be greatfull for any ideas. it will be crucial for SSc5.1 and as building is located on very little plot, so I would rather avoid any miscalculations.