Good point scorch. MANY years ago I qualified for Rifle and Shotgun merit badge on 'sketos and a smooth bore rifle; breaking them at about 40 feet with no problem. But put the shot shell in a rifled barrel and they wouldn't break a 'sketo sitting on a post at 25 feet. - Good memories.
Personally, I would not fire any .22 non-shot (i.e. bullet) at a roof. It is a puncture waiting to happen. And that's irrespective of the safety concerns of firing a bullet skyward.
My 2 cents,
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