I hate getting back to airplanes, but it's what I know.
Many, many Experimental homebuilts are built, well, many more are started than are finished, but I bet that is the same for boats.
If you want an airplane to fly, buy a production airplane.
If you love designing and building, and flying would be nice, but the real love is the building, then build a home built.
I bet it's the same for boats, if you want to sail, buy a ready to sail boat