is this used for a business? If not, you can't deduct it at all. If used for a business, you will start reporting it in 2020, once it is built and you start using it for business, You will take all costs spent in construction materials, labor, sales tax, building permits etc and add these all together. This becomes the depreciable basis in your property and is used as a basis to begin taking depreciated expense in your taxes. It is what we in the tax business call a Depreciable Asset.