Underground car parking

Hi, we are dealing with new LEED hospitality project. The project will be constructed in two stages (two towers), with common parking under both of them constructed in the first stage. The garage will have one car entry and will serve both towers. Developer decided to certified the I stage of project and he is willing to keep possibility of certifying in future the second stage. We are wondering how to deal and assign in proper way the project boundary for this project for both certifications. Any help will be appreciated.