If you've signed an office lease, you know that your rent isn't really your rent. In some buildings, you pay operating costs on top of your rent. You're probably aware of the load factor that makes you pay for your office space and for what the landlord considers your "fair" share of the common areas of the building. And you might also have to pay for parking. But there could be even more hidden costs lurking in your office lease. Work with your tenant representative to see if you could be on the hook for any of these five additional expenses.