You will need to model some of the whole building characteristics, which will vary depending on the project. Portions of the base building that serve the project space will need to be included in the table. Exactly what you model will depend on many factors. In many projects, only a portion of the HVAC system serves the tenant space. In such cases, a percentage of the shared system can be allocated to the project space. The methodology to allocate the systems is explained in the LEED Reference Guide.