Which rating system

Our client is developing an office project consisting of three office towers with a common open plan ground floor and two common basement parking floors. The first of the tower has already been built (not LEED-certified), as well as the two common basement parking floors. Our client is now interested in getting a LEED-certificate for the second tower, which construction works are soon about to start. The third tower will be built later on (no decision regarding LEED). Which rating system would be the best in this case? How do we draw the project boundary, considering that the ground floor (open plan retail space) and the basement parking floors are common to all three office buildings? The three buildings will mostly have their own mechanical systems, but there will be some common technical spaces in the basement. Is it possible to create a master site for the whole project and apply for LEED for the second office tower only? Can the ground floor and the basements somehow be excluded, since drawing a project boundary is difficult?