Query on Works Contract

My client is a pvt. ltd. co.. One Mr. S received a contract from Indian Oil for industrial construction. Mr. Singh in turn contracted out the work to our client. In this work, we had to use materials and labour on our cost and bear all other related expenses, Mr. S gave us a lump sum amount for carrying out the work. After the work is completed we raise the bill on Mr. S. the billed amount includes material cost, labour cost etc., but this break up (i.e. what % is material cost, what % is labour cost etc.) is not shown.

Sir, the query is that should we charge Service Tax on the bill raised to Mr. S, and if yes then at what rate.

Sir, we charge a single bill on the work.
Is the composite scheme where Ser tax @ 2% is charged applicable.