As I understand your question, recognition of revenue based on the stage of completion is one aspect and the recognition of the relevant cost of sales is another aspect. Stage of completion can be decided on many methods as given in IAS 18.24. Even if you do not recognize labour cost so far incurred as inventories, you will have to consider it as WIP in deciding the profit of the project. Note that IAS 2.37 says "The inventories of a service provider may be described as work in progress"