Very urgent service tax query

ours a construction co, involved in building residential complex. as per the practice in the industries, after a certain amount of work has been done , we issue a running bill to the client(which takes around a period 15 days to assess by our engineers) after issuing the bill to the client. it takes some time bby the client to certify the work done(15 dys) and after that the payment is released with certain deductions and with retention money and security. my question is how the new service tax rules will apply on this case.