Valuation method for service tax

I have to take service tax registration no. for pvt. ltd co. providing services in building commercial /residential complexes.

1. on what amount service tax   to be paid...on  advance amount or gorss value???

2. please give the valuation method for commercial and residential complex service in whch service tax paid @ 10.3% on value of service - material & land or additional service + profit margin ?????



is it as per CAS(cost accounting standard)-4 or any specified method as per CBEC ???