A lot of tradespeople are not clear on the differences between common property and the lot (neither are many owners for that matter!) If you have a managing agent it is best to get them involved in engaging the contractor for any work carried out. The agent should send a numbered order form to the contractor which clearly sets out the work agreed to and the price, and tells the contractor where to submit the account. Make sure though that your managing agent checks with you that the work has been performed properly before he/she pays the account. Unfortunately if owners or an executive committee take it on themselves to order work on common property they can become personally liable in the event of a dispute over payment or the quality of work performed.