Deductions & credits

Interesting question.

 

My first thought is that you sold TWO things:  Land and the building.  As such, the land would be when the lot was purchased.  For the building, there is no difference on the tax return for selling a 2nd "home" versus just a "building".  So because you are selling the "buiding" (rather than a "home") I would use the date that the building was finished.