Hello,
You can approach your registrar and get a valuation certificate for your property as on 01st April 2001. Index that valuation and calculate the value as on the date of sale.
For the construction, obviously you will need documentary evidences to substantiate your cost of construction or else it will get very difficult claiming the same.
Atleast provide the registrar valuation of your property as on 01st April 2001 to help us guide you ways in order to plan your taxes.
Trust this clarifies your query.
Feel free to call / get back in case of further clarifications.
Thanking You.
Regards,
Rohit R Sharma
BCOM, ACA, LLB-GEN, CERT. FAFP