LTCG ON SALE ON LAND AND BUILIDNG

One thing for sure is that s. 50C would apply in this case and your sale consideration will be 20.5 lacs instead of 18 lacs

Hi even if you sell it at 18 L you will have to pay LTCG as under section 50 C the diff between sdv and sale consideration shall not exceed 10% so in this case 18L *110% = 19.8 L while computing LTCG 20 L would be considered as Sale consideration ..
For LTCG please specify the purchase price as indexation will apply taking year 2000-2001 as base year

Thanks, both of you. I need to know how easily I can calculate the cost of acquisitions as of 1-4-2001. It is old property documentation of building cost that has not been done. 

(e.g. stamp duty as of 1-4-2001 and from where I can get the stamp duty) 

You need to get the property valued by a certified valuer. you may approach any CA or Advocate. They might have some valuer in their contact. the valuer will give value for the year 2000-01 and thereafter you will get indexation benefit.

Whether a certified valuer report is compulsory (section or guideline). can I take stamp duty value (1-4-2001) as the cost of acquisition?

I am not sure about that.

If you dont have the paper its better to have a strong proof like a valuation certificate..