"I'd be really angry to be blasted awake like that at 7:30 AM on a weekend. On a weekend, I think 10 AM is reasonable, or I'd possibly accept 9, grudgingly, but before 9 is really, really inconsiderate. It's aggravating enough on a weekday (not everyone works a 9 to 5 job and gets up at 7 every morning) but I'm willing to accept that that's the way things are during the week. On the weekend I expect to be allowed to sleep in a bit."
But on the other hand, if it was your roof and not starting until 10 meant you had to have the builders there for another day, and the risk of a heavy snow fall on an unfinished roof, wouldn't you want them to get going as soon as possible.
A thing like this is a one-off event, not continuous every-single-day noise, so shouldn't we all be understanding of the situation and cope with being woken a little early for a few days. Just get up and enjoy the extra time, or put on some music and roll over and go back to sleep. Quite honestly I can't see that there's a lot of difference in feel between waking at 7.30 and 8 so for half an hour's sleep it's a bit petty, and of course you could always go to bed a little earlier if that 30 minutes is so important to your wellbeing.