Vat rate for work contractor

Dear Expert,

We are a Work Contractor of NTPC in Bihar. Our Work is Fabrication, Eraction and Other Civil Work. Client Deduct 5% WCT.

at the Time of Filing Return we Deduct Store Consumable and Labour Charges from Total Turnover to Get taxable Turnover and Divide the Taxable turnover in Propertion of Construction Material Used i.e. 5% and 13.5% and Get our tax Liabilty.

But My Sales tax Consultant ask me to pay 13.5% Vat on all Taxable turnover. so i want to know are there any specified vat rate for a work contractor.