Shared parking deck

We have a campus being constructed with 5 expected buildings and 1 parking deck to serve all. All buildings and deck will be individually metered. We are planning a campus approach. We are trying to determine how to account for the parking deck energy usage? Currently 3 buildings and the deck are being constructed. The other two will be constructed at a later date. To account for the parking deck energy in the EA modeling credits we are planning to pro-rate deck energy usage by sq ft and assign that to each building. Is this the best way to calculate? For example: 1 building accounts for 46% of total campus sq ft and we will add 46% of the parking deck energy usage to this building's energy model.