This article will show you how to build a cheap fully functioning windmill. You will need to find the materials for the tail prop and blades before you actually begin constructing the bicycle wheel windmill. This example uses five plexiglass blades which are cut with a utility knife in the shape of blades. These blades are 4" at the top, slimming to 2" bottom. The tops are rounded and the overall length results in a 20" blade. The prop used here is also constructed out of plexiglass (20" by 4").