Even this, his 'play-yard', is somewhat supervised. I won't beat a dead horse here; longtime readers know my opinions and experience. Parents, you've got to let go. We used to climb on the parapets of the buildings at Princeton University, 80 feet and more in the air. The most valuable life lessons were learned away from grownups, away from authority ... out on our own.
And no, kids don't fall off roofs. Adults do, kids don't.