The joint research by Kenzo Tange and Frei Otto, which may have significantly influenced the roof design of the Mannheim Multipurpose Hall by Frei Otto, is only mentioned by name, and there is no analysis of how the results of the research have been developed. Therefore, this study aims to clarify the influence of the joint research on the roof shape of the Mannheim Multipurpose Hall, based on the book IL10, which summarizes the joint research. The analysis clarified the following two points. First, the roof shape of the Mannheim Multipurpose Hall strongly reflects the results of the joint research in various grid shell-forming elements, such as the mesh shape and suspension form, as well as the chain net of the suspension model experiment. Second, the roof shape was not planned according to the plan shape but according to the optimization of the grid shell. In addition, decisions on the mesh shape and hanging form were made to develop an ideal lightweight structure by optimizing the grid shell. Therefore, the lightweight structure pursued by Otto was realized owing to the results of the joint research.