if having someone rent the equivalent of a garden shed is all legal in the US, then they only need a few 'fools' willing to forgo 50% of rent to get rich.

It is really quite cheap to build a shed (a few thousand in materials and it's really not that hard. construction companies are not cheap, but since people build sheds themselves all the time you would not really need them.

in most non-US jurisdictions, this would not be legal. a father of a friend did this and the govt kindly requested him to force out his tenant.