The cooperative has the right to purchase real estate for the purpose of erecting, owning, and operating apartment houses or apartment buildings. The interest of each individual member in the cooperative shall be evidenced by the issuance of a certificate of membership. The certificate of membership is coupled with a possessory interest in the real and personal property of the cooperative, entitling each member to a proprietary lease with the cooperative under which each member has an exclusive possessory interest in an apartment unit and a possessory interest in common with all other members in that portion of the cooperative’s real and personal property not constituting apartment units, and which creates a legal relationship of landlord and tenant between the cooperative and member. The certificate of membership shall be executed by the president of the cooperative and attested by its secretary in the name and in the behalf of the cooperative.