It is the Owners Corporation who is entering into the contract for the work, not you. Owners Corporations have a legal personality so they can enter into contracts, that is why they have a seal. Of course you don’t always have to enter into a written agreement, but the principle applies across the board.
So for any work it should be made clear that it is being done for the OC, and that the invoice is issued in the name of the OC as the contracting party. Aside from anything else, that won’t leave you with the debt in the event that the OC refuses to pay (unlikely but going by the stories on here I am sure it happens)