Capital gain tax on sale of flat developed on ancestral land

Dear Madam/Sir, 

I inherited a piece of land with a dilapidated building( almost 100 years old) on it . I gave it to a developer. The dilapidated building was demolished and flats were constructed by developer.Per agreement I got 2 flats( being 40% of the total carpet area generated.. He is free to sell other flats( 60% of carpet area).. I did not pay him any capital for construction of these flats. He  did everything. If I sell these two flats, will capital gains tax be applicable? For example if I sell flat for say 40 Lakh,  it is not the whole gain to me as developer has spent money on the plot of land to construct the flats. Only after this investment the cast of flat is 40 lakh.( ie cost of land +cost of construction). Plus I have forgone 60% of carpet area. How to quantify the  Capital gained as value has been added to the land before being put up for sale?

I have no flat in my name in anyother place.

Kindly enlighten.

Thanks, 

Sincere regards, 

Sadan Kumar Sinha,

Navi Mumbai