such person so using the tangible personal property shall pay the tax levied in this section on the fair market value of such tangible personal property when used, without any deductions whatsoever; provided, that this subsection (a) shall not be construed to apply to contractors or subcontractors who fabricate, erect or apply tangible personal property that becomes a component part of a building, and that is not sold by them as a manufactured item.
T.C.A. § 67-6-209