I've done some roofing in my years with the county.......but....
Saw this while walking in my coffee village yesterday.
On the other side ( a straight drop to the ground) was a guy tethered doing the nailing, with a kid above him standing on a 2x4 dropping shingles down to him. This kid did not appear to be tethered.
I went through two auto-rotations in Vietnam - so, not crazy about heights as a result.
Stig