If you live in the US, the best place to start is with a junkyard chassis, because if you have a VIN, all else is possible.
If you want to go REALLY nuts, you can effectively create a sandrail type custom vehicle, but it’ll never* be allowed on freeways
(it’s not impossible, but the regulations and testing is a bit excessive)
I would like to build my own car but have no idea where to start.
If you live in the US, the best place to start is with a junkyard chassis, because if you have a VIN, all else is possible. If you want to go REALLY nuts, you can effectively create a sandrail type custom vehicle, but it’ll never* be allowed on freeways
(it’s not impossible, but the regulations and testing is a bit excessive)
Depends on your end goal but I would start by working as an engineer in any sized car company