They were on his lawn, of course.
"Get off my lawn, you damn kids!"
I can appreciate responding armed to strangers in your backyard (if they were indeed in the backyard; to inspect a roof I would imagine you would have to be).
Gun in hand or in holster.
Not necessarily pointed at anyone though.
Certainly not encouraging a speedy departure with a boolit though. Sounds like he is getting what he deserved.