ahem. fit proper steering. wheels. chassis. then all the annoying little accessories... handbrake, lights, indicators, seats, a shell.... making sure all these are up to standards and the correct heights from the ground and distance apart... maybe seatbelts, a rollcage and airbags. cus those standards these days on new vehicles require such things.
then an engineers certificate with no mention that it started life as a skateboard, and youre good to go? maybe...you could do it here i guess...