For the purpose of this chapter, a "residential builder" is one who constructs a residential building or structure for sale or who, for a fixed price, commission, fee, or wage, undertakes or offers to undertake the construction or superintending of the construction of any building or structure which is not over three floors in height and which does not have more than sixteen units in the apartment complex, or the repair, improvement, or reimprovement thereof, to be used by another as a residence when the cost of the undertaking exceeds five thousand dollars. Nothing in this chapter prevents any person, or his agents, from performing these acts on his own residence or on his other real estate held for personal or rental, as opposed to speculative, purposes. Anyone who engages or offers to engage in such undertaking in this State is considered to have engaged in the business of residential building.