This will be easiest on a map with no other blocks. You can start a new world from the pause menu. The first thing you want to do is pause, and in the menu select "grid". This will place a grid across the map.
Next you want to hold
to zoom out as far as possible. You are looking for a perfect star shape in the grid, took me about 5-10 minutes to find my first one. You will know its the right shape when you build around it will be a pretty much perfect circle.
You want to build 2 buildings high in a circle shape around the star with nothing in the middle. Then delete the bottom row of buildings.
You will know you did it right when the 2nd row is on propellers instead of stilts like normal. As far as I'm aware it NEEDS to be built around the star/circle formation.