In order to properly determine the respective rights & obligations of the parties, you should consider having your lease & the signed contracts reviewed by an attorney who is experienced in this area of law. Generally the lease & lease rider & lease rules & regulations, if any, will govern a tenant's rights & obligations regarding the use of a common area. Since you were asked to sign a separate contract, which provides that certain requirements be met as a condition precedent to the use of the rooftop, that contract may or may not be enforceable, once there has been a proper legal analysis of the lease, the contract & the applicable law. Good luck!