Sales of building materials to a contractor or speculative builder for the construction, maintenance or repair of commercial property or any other property not excepted in section 3(n) of the Act, as explained above, will be considered as sales for resale. (See §§ 779.332 and 779.335.) Some employers who are dealers in building materials are also engaged in the business of building contractors or speculative builders. Building materials for the carrying on of the employer's contracting or speculative building business often are supplied by the employer himself from or through his building materials establishment. In the analysis of the sales of the building materials establishment for the purpose of determining the qualification of such establishment as a “retail or service establishment” all transfers of stock made by the employer from or through his building materials establishment to his building business for the construction, maintenance or repair of commercial property or any other property not excepted in section 3 (n) of the Act will be considered as sales made by such establishment for resale.