How do you get a custom motor bike registered?

depends, if its from a licensed dealer, you pay at time of purchase, however, if you plan on building one yourself you will need to keep m.s.o's of frame,motor,and transmission. depending on the state you live in, there will be safety and equipment requirements the bike will need. for example: in my home state of Arizona, required safety equipment is simply a headlight,tailight, and 1 rear view mirror. once its gone through inspection at d.m.v. and your documents are in order you will receive the title as a special construction motorcycle and will now be able to register,get your plates, and can roll away and have a friend take your vehicle that trailered the bike to d.m.v. back home.