Recent studies on the optimum design of pre-engineered building structures are much advanced due to the continuous effort to improve the marketability of steel structures with the increased concern for steel structures. In this paper, a computer software was developed for the optimum weight design of 3-D structure built with nonprismatic H-shaped steel members using the AISC code. The constraints for optimizing design of structures are member forces, member depth limits, restraint conditions for members, member connectivities, member groups, displacement limits for the structure, plate thickness limits and etc. The design results with this self-optimizing design software show that optimum members can be determined after 7-10 iterations of the optimizing design process, and the weight of structure designed with nonprismatic steel members could be reduced considerablely comparing with that with prismatic members only.