We introduce a new method of shape modeling using homotopy and object-oriented modeling. Homotopy is a kind of topology that gives more general ideas of preserving invariant properties of geometrical objects and is further expanded to conceptual objects. The conventional shape modeling using polygonalization has serious difficulties in preserving invariant properties, leading to the necessity of a massive amount of data. On the other hand, the combination of homotopy and object-oriented modeling, which uses class hierarchy, help preserve invariant properties at all abstraction levels. We will explain how our new method will help us preserve invariant properties, which keeps the amount of data to the minimum possible level, using an example of a tennis ball rolling on a slope.