Stamp paper required for booking of flat of the amounts of above rs. 20,000/- in kolkata

Dear sir/madam, You are requested to provide me the slab of the stamp to be used for cash/cheque transaction in west bengal. A flat to be booked and amounts may be fluctuated. So, I need the slab for making the agreement. Approx booking money may be Rs. 30,000/- and the price of the flat is 31,00,000. After searching and surveying within one month for the loan to purchase the flat, if purchase of the flat will be rejected booking money will be refunded. Also I'll be grateful if anyone suggest me for the necessary action to be taken for the agreement.