@chuckjim
You don't need to use the calculator if you know the basis. If the grandparents didn't pay for the land, then you have no basis in the land, and your only basis is what you paid to build the house. "Bought" for the cost of building is adequate for tax purposes. You can't take depreciation unless the house was used for business or as a rental, if it was, you must follow through with that because you have pay tax on (recapture) the previous depreciation.
The questions about a loss relate to possible deduction of a casualty loss, or receipt of an insurance payment without rebuilding, since those things adjust your basis. As long as you used the insurance to rebuild, then the gain from the rebuilding cancels out the loss from the fire and you can go ahead and say you don't have a loss.
