I bet more than one reader of this group (maybe the homebuilt group)
could
hack something together in no time.
It would then be reasonably easy to get it certified as experimental.
What about certified to drive on the road?
Keep in mind the golf carts that are road legal...

I've been in the homebuilding world since 1973 and can think
of a half-dozen attempts to build a roadable car. NONE of them were
worth pursuing. They were heavy, flew rather poorly and most were
rotten as cars. Some of them killed their designers. The added
mechanism to gear an engine to wheels adds a lot of weight any way you
look at it, and the engine, if it's aircooled, has to have a fan. More
weight. The cumbersome wings and tail take time to remove and install,
and a simple mistake in assembly can kill. There was one, a delta sort
of layout, that had folding wings that bent twice and shielded the
pusher prop. More heavy mechanisms. IIRC the designer couldn't get any
road licensing with that prop driving the "car." Too dangerous. Imagine
the reaction of an insurance company! Another one, a Ford Pinto married
to the aft section of a Cessna 337, actually flew. The airplane section
was unbolted and left at the airport while the car ran around town. The
whole thing was too heavy, and one day the car fell off in flight. End
of experiment.
People with big ideas about building flying cars should do
their research and learn a lot before trying to persuade someone that
it's easy. There have been many mistakes make and the ignorant will
only make them again. The simple fact is that airplanes are meant to
fly and cars are meant to drive, and because of the technological
requirements the two don't fit together well in one machine at all.

Dan