1. Determine the purpose of the car: If you will be using the car for long distance highway travel or for a short weekend getaway, for example, this will have an impact on the design. 2. Consider the type of engine: Depending on what kind of power you would like the car to have, you will need to decide between a gasoline, diesel or electric engine. 3. Design the exterior: You will need to decide on the size and shape of the car, as well as the type of materials and features you would like to incorporate. 4. Design the interior: Decide on the seating and storage arrangements that you feel are necessary, as well as the types of materials and features you would like to include. 5. Finalize the design: Once you have worked out all the details, you will need to create a prototype of the car and test it to make sure it meets your requirements.