Taxation on jda

Q1. When does the tax liability occure in JD Aggreement? Is it at the time of signing JDA or after completion of Apartment? How is liable to deduct TDS in JDA?

Q2. Owner gets demeed sale consideration in the form of 2 Flats. And owner retains 1Flat for his residence and proposes to sell the other.

In the above case,can owner claim cost of construction on that Flat? If not, reasons? Other provision to reduce tax in this capital gains.