Service tax on flats

I baught a flat at a cost of Rs 9 lacs, my builder has reistered the flat under prakoshth adhiniyam as undivided share in a common land at rs 3 lacs , and he has made aseparate agreement for construction of flat with me for 6 lacs, how much service tax is payable and how can i know the exact amount of tax he has paid in respect of my flat