Long term capital gain on sale of flats

Hi,

One of my Client has purchased the site in 2004-05. As per the Joint Venture agreement, he had given the site to some builder to construct the flat on his site. In return, my client got 4 flats.

Now for the current year, he sold 3 flats.

My question is,

1) At what point do the long term capital gain will arise, is it when he gave the site in return of flat or when he actually sold his flats in 2010-11.

2) What should be the cost that should be taken for indexation. (Is that site cost+construction cost)

3) What should the sale consideration comprise of?

Regards

Lakshmi Devanand