A drainage system design method and apparatus including a computer program that enables a computer user to design and obtain computer-generated stackings of drainage system structures such as manholes. The user inputs dimensional and structural information concerning the drainage system. The program is operable to access a set of predefined drainage system components and, using the inputted dimensional and structural information, the program determines different configurations of the predefined components that represent a structure contained in the drainage system. The program displays different configurations of stackings sorted based on predefined goodness criteria. The program can also determine one or more drainage system designs that comprise a configuration of the predefined components for each of two or more of the structures contained in the drainage system, and can display and output site plans, elevational views, shop drawings, and bills of material.