I want to build my own windmill for electricity
Maybe try Popular Mechanics or another such source. Don't forget that you actually want to construct this thing in a safe and suitable manner. Maybe place some calls to companies that make wind energy windmills for personal usage, such as powering a small house, etc. Say that it us for a small school project. You might be surprised, as they might want to help you out with suggestions and the like.
usually not an AC motor since they do not have magnets. Magnetism for those are generated by electricity. Most DC motors have magnets and thus can be used. You could use a car alternator as one. Farmers have done thing like this for years. wind mill to car alternator fed to a battery charger to battery. Don't forget the charger or you will have a battery turning a big fan
