Here's how the self-built vehicle thing could work.
Four sets of wheels, wings, and curved upside-down ramps and seat bricks
(ramps for boats wheels for land vehicles and wings are loving obvious)
CREATION
Plant four wheel bricks and put them together via blocks. On every brick plant, the console/syntax will update a "brickmap" to see if a vehicle structure has been created. A valid vehicle structure for a car would have atleast two wheels and a seat connected to it via bricks. After a proper car skeleton has been made, and you have no items in your hook/hand (e.g. gun, printer, brick placer, etc) you can ride in it. Right clicking shall also be the way out of the vehicle.
CUSTOMIZATION
After a valid skeletal vehicle has been built, you could then build on it (when there is no driver and it is in brick-mode.
HOW IT WOULD WORK
This one is probably the most challenging to do, but only for the people making the mod/but only for kompresser/badspot. The syntax, when detecting a valid vehicle, will save it's design every time it gets changed. When the vehicle is being driven around, it cannot be stopped/parked/left when facing diagonally. When it's near aligned with the terrain/bricks/etc below it, and the player leaves the vehicle, the vehicle will revert into actual bricks (via syntax using the saved data), along with it facing the nearest direction the vehicle was parked at.
(lolforgetJVScompatibilityonth evehicles)