3D ancient building models for reconstructing historical structures are expected to be utilized in various academic fields, including "Historical Preservation" based on the excavation of ancient ruins, "Archaeological Research and Studies" aimed at better understanding archaeological findings, and "Tourism Promotion." Moreover, 3D building models can also be applied to research in "Urban Form and Digital Architecture." However, 3D modeling currently requires significant effort and time. Therefore, this study developed an application for the automatic generation of ancient buildings, such as ancient castles, multi-tiered pagodas, and traditional gates. In particular, we propose a method for the flexible placement of components—such as windows, doors, and wooden partial walls—within the unit spaces between columns in ancient castles. Additionally, to model complex architectural elements like "Kumimono" (bracket complexes beneath eaves), which cannot be accurately created using conventional Constructive Solid Geometry (CSG) methods alone, we introduce a novel technique. This approach first involves extruding the outer contour of the structure as viewed from one direction. A second extrusion is then performed based on the contour from a perpendicular viewpoint. Finally, a Boolean operation is applied between the two extrusions to precisely construct the "Kumimono" geometry.