How to pass entries in petty contractor account

Dear Sir,

We are in construction work, we are engaged with a petty contractor for electrical fitting work with material for Rs. 5,00,000/-  total contract value, out of 5,00,000/- we purchased on the behalf of petty contractor for material Rs. 3,00,000/- which is paid to supplier directly and the bill raised by supplier on behalf of us. Now we paid to the petty contractor  rest amount 2,00,000/-. How to pass the entries in our book including purchase entries from supplier.

Please help us, thanks