The criteria for professional service and contractual service in your case would be:- Whether you are giving him drawings etc., or not. I you should decide.
If you are not giving drawings and the job executed 'really ' demands professional skill then it is a professional service.
If you are giving drawings etc. (and can prove beyond doubt) then it is surely contractual service.
Again we being Indians take a decision like a cat on the wall then:-
If the value of the contract is only few lakhs -say 2-3 lakhs then you can say though by nature it is called interior work by nature the job done does not demand any professionalism and purely depending on the oral instructions of manager / owner the job is done.(as it can be done by any carpenter) then it is a contract.
If the value of job itself is of good amount say >25 / 30 lakhs then you can not argue like this. It is certainly a professional job.
(The above inference isn drawn after reading various cases pertaining to applicability of service tax + I have good no. of clients who are sub contractors to leading architects. The architets after consultation with their CAs agreed to the above line of thought and said that the architects who got the contract are rendering professional service the sub contractors and the service rendered by sub contractors who does not possess any recognised qualification cannot be professional job. They are only doing under the guidance of professionals.)
Any how wait for more comments.