The builder was the guy who built the house on the wrong land. Legally, the landowner could claim a free house.
There's legal, and there's what is done.
In my neck of the woods, that house would last two-three years tops before a "mysterious fire" erased the gains of the chortling landowner who got the labor for free.
Try to get the labor AND the materials for free? Just asking for trouble.
Yeah, yeah - I know the builder was a buffoon. I would hope the new homeowner/landowner would tread that minefield carefully.