This paper examines the application of Evolver, a genetic algorithm (GA) solving program, in a three-parameter optimization of a steel truss floor system with a concrete slab floor deck. The floor system is comprised of truss girders supporting beams running in a direction perpendicular to the truss girders with a composite floor deck along the top. Using Evolver, three parameters are optimized for two truss girder topologies in order to find the least cost floor system. The weight of the structural members is correlated to the expenses of material, labor, equipment, overhead, and profit required for the construction of the floor through information given by Means Building Construction Cost Data and interviews with steel fabricators. This procedure may be modified to optimize the cost of any floor area that may use different truss girder topologies, beam sections, and connections. Parametric optimization is defined in this paper as the combination of configuration, size, and topology optimization of a truss girder, the size optimization of beams, and the optimization of the spacings of both beams and truss girders in the system.