Ltcg u/s 54 for ancestral house under devp agreement

Different options can be tried........... but any valuation certificate from Municipal authority about the value of the property as on 1994 would be more authentic.........

Thanks!

May be purchase agreements of others in the same building can be used as reference for prevailing at that time market value? Also ready reckoner rate at that time can be another reference point. 
Do you think construction cost in 1994 would become basis for purchase price in such cases?  

Only construction cost will not help, as it will not include the cost of land........

Another option is based on development agreement, but it will be more tedious way. Rather than that go for valuation certificate from Government valuer, which cannot be questioned otherwise .....