I lived on the property for 26 years and build new structure on it in the time and now sold it. . Where can I deduct cost of building new structure?

I assume your home was on this property and that the new structure was a garage, a workshop, an in-law residence or something else that you used personally.

You simply add the cost of building that new structure to your adjusted basis for the original property you sold.

Tom Young

That was replacement house, when the old one was demolished.

The answer's the same.  It gets added to the adjusted basis of the property you sold.