Capital gains

Purchased land in financial year 1994-95 and constructed in same financial year but no bill available for cost incurred in construction. Also in 2013-2014 two more rooms are constructed but no bill available for the same. since the owner of the house constructed house without taking the service of any builder and also  not involving work contract so no bill are available. expenditure incurred in cash paid to casual labour on daily basis and no record available for cost of material used in construction. owner of the house sold the house in FY 2015-16 so my question is how to calculate the cost of acquisiton in 1994-95 and cost of improvement 2013-14 for the purpose of calculating capital gains?