Cost of construction

A land was purchased in 2005-06. The registration document of that is available. Then construction was done on that plot in same year but all the bills of that are lost.
In the absence of bills how to take cost of construction as now that residential property is to be hold. Is there some notifications on this?. Can I take value of construction on the basis of bank statements or amount remember by me. What proof can I give if I get any query from income tax department