Have an idea what you want it to do, first. Then figure out how you’re going to achieve that aim. Taking into account potential problems etc. Get other people, who have experience of designing bikes, to give you advice. Maybe talk to them, and get them to knock up a few prototypes. Iron out the little problems, until you have something you feel is ‘right’.
It’s really not rocket science, it’s fairly low-level engineering, really.
Then find a big **** off Taiwanese factory who can knock them out for you at £25 a pop, sell for £150- Job’s a good un! 😉
I might give it a go, actually. Then get a lucrative tie-in with Cannondale, to produce the Rude Boy. Like a Bad Boy, but ruder…