If you think that the only occupancy cost that matters is rent, you could be in for a big surprise. The net rent that you pay is only a small part of the cost of occupying commercial real estate space. Not only can the other costs add up to more of your rent, but they can also be unpredictable from year to year. Beyond the Common Area Maintenance (CAM) charges that many buildings levy, here are some of the line items that could apply to your business.