Virtual reality and digital twin for construction and urban planning needs 3D city models which contain multiple 3D building models. It takes lots of time to create 3D buildings. In order to automate laborious steps, a GIS and CG–integrated system is proposed for automatically generating 3D building models, based on building polygons (building footprints) on digital maps. Digital maps show most building polygons’ edges meet at right angles (orthogonal polygon). An orthogonal polygon can be partitioned into a set of divided rectangles. We demonstrate an automatic generation of “Step-Shaped Building” by allocating different stories to divided rectangles. In this paper, we conceptualize a building polygon as a “tree structure” comprised of divided rectangles. The floor numbers assigned to each divided rectangle are determined by its “layer” within the tree structure, enabling the automatic generation of step-shaped buildings. In this paper, we also show automatic generation of the buildings whose façade are versatile and uneven, being added detailed undulations to the façade. To draw these detailed undulations, this study is introducing the concept of “drawing points” with “statuses.” A step-shaped building can be a promising candidate for a “sustainable building” by implementing rooftop greening and installing solar panels on balconies.