Wow. Lots of discussion regarding how many angels can dance on the head of a pin here.
Seems that there is no dispute that 1) there is no known legal bar to a suit againt the amature builder for construction defects, 2) that there seems to be little empirical evidence that these suits occur anything but rarely.
I would just add that there are a lot of reasons why such claims would not make their way all the way up to a reported decision. Understanding that plaintiffs' lawyers want money, not justice, they would prefer a settlement to a trial, they would prefer a judgment against a solvant/deep pocket defendant (preferably one with insurance) rather than an individual, and they don't care what theory they get the judgment on.
In order to see a reported amature built liability case, you would need 1) an accident, 2) involving an allegedly defective aircraft, 3) involving an aircraft that was sold (if it hadn't been sold, they would probably just sue the owner based on his pilot operations (or would at least include that as part of the claim) because that would likely be an insured risk), 4) causing harm to a third party (I am assuming generally the purchaser would have a big uphill battle given likely waiver forms, and assumption of the risk issues, 5) the harm was large enough to warrant pursuit of an expensive lawsuit, 6) the aircraft was less than the 18 years of GARA, as well as what ever statute of repose would apply under the applicable state law (my state, for example, has a 10 year statute of repose.), and 7) there is no settlement. How often has this fact pattern actually occured? Of course, that it rarely if ever has occured doesn't mean it couldn't happen today.