I designed this kingdom generator for my new world of Khodax.
Step one, on a piece of engineering graph paper draw a regional map to the scale of 20 miles per square. Include major geological features like rivers, forests, hills and mountains.
Kingdom Size: Roll 1d100 x 10 square miles (You can adjust this to create larger or smaller kingdoms.) After you calculate the square mileage of the kingdom, have the PC outline on the map where his borders will be.