Leakage in my flat from privately owned terrace.

Over my flat there is a flat with an open terrace owned by the flat owner.Due to heavy leakage from the terrace my flat ceiling is badly damaged. I would like to know who would be responsible for the payment of the repairs, the terrace owners, society or me. In spite of efforts the water proofing is not done properly, what are my options? Thanks, Vaishali