Whole building climate control doesn't mean all units are set to the same temperature! The discussion is specifically about a zoning hvac systems and billing for them.

HVAC systems unfortunately don't work as nicely as you describe. You can't run the HVAC for just one unit, typically buildings are broken down into floors and either the system for the floor is on or off. This is how you see multi-tenant offices designed -- each floor is submetered and the cost is divided proportionally among the tenants on that floor based on square footage. The zoning works by controlling airflow in the ducts. So while your billing system is clever it would be absolute murder if you were the only one running AC/Heat and you would be much better off with a smaller individual unit.