You can do what someone else did in this group - start you own project with the CAD software of your choice and have others join in.
You can support the projects that are already in progress.
But in either case you need to understand the vehicle codes for which country you are designing it for. Certain countries will not allow speeds for bicycles to be over 20 miles per hour and it is illegal to do so. It may also risk killing the rider or pedestrians that don't expect you to go that fast.
For vehicles over 20 mph, you are now having to abide by the vehicles codes and design for compliance to their specifications and every country is different.
But the basics are a vehicle, an electric motor, the batteries, the speed control, the battery charger, and other drive electronics.
Other parts more common like the brakes, suspension, steering, wheels, tires, ... etc can be just used whatever is already available and in use.
Please read all the articles that I posted to this group to give you a flavor of the wide variety and costs of electric 2-wheelers already out there. If you want to create something original, make sure that you have a purpose in mind for street, off-road, farm work, racing, ... etc as the design needs will be focused for that application.