Your cost basis is what you actually paid for land, materials and subcontractors. You can also include required fees for building permits, utility hook-up, and so on. You can't include anything for the value of your time and effort. You can also review publication 523.
https://www.irs.gov/pub/irs-pdf/p523.pdf
The tax value is not acceptable. Even if you had a valid real estate appraisal, that is not the same as the cost basis. Any appraisal of the value of the whole house would necessarily include intangibles, such as location, style, and the value of your labor. Your cost basis is only what you can prove you actually paid out of pocket.
Also be aware that, if audited, the IRS does not have to award any cost basis you can't prove, and they are legally allowed to assign a cost basis of zero if you can't prove your costs to their satisfaction.
