Capital gains

When were the flats received by you? What was tax treatment at the time of handing over of the plot to builder?

It is correlated to these factors, but rough answer is take circle rate for 5 flats received by you for calculation of LTCG over plot. Any additional amount (market rate) over the sell of two flats can be taken as STCG.

   You may maintain the necessary documentation/registration with respect to the gift transaction.

This is when u received properity as gift 

    Now with the help of promotor an apartment has been constructed thereon and out of which five flats have been given to u

        so the date when u received the flats is important  and u want to sales them so take  purchase prise of that flat 

as per recknor when your receive it and ltcg or stcg depend upon the period between buying and selling of flat