Capital Gain Query

My uncle have two nos of land value 4Lakh & 1Lakh, purchase in 2003 & 1994 respectively.
He made agreement with Promoter in 2014, promoter will give 3 flats, 1 Office area and 2 Lakh in Cash in consideration against land.
But during construction it is found that few extra area made, my uncle is paying Rs.7 lakh for that extra area, In 2015-16 & 2016-17 and Rs.1lakh is due, will be paid at the time of possession. What will be capital gain implication. My uncle have Business. Plz suggest.