Construction contracts

As per the contract, a project has to be delivered, and then for a period of 2 years a retention amount is held for 10%of the contract value approximately, and 60%is received as advance and 30% is received on the completion of the project. after the completion the 90% will be recorded as revenue, 60 % as revenue across period and the 30% at the point of time. the 10%, what is the double entry for it ..please kindly help