Typically contractors and subcontractors are paid by the job, not hour. Yes, it's definitely considered difficult labor, but again, the body adapts and strengthens. I wouldn't suggest working in 100 degree sun, however, that's just crazy.
Average roofer pay is 18.53, average amazon warehouse pay is 13.50. Good roofers in a hot market (currently) can get well over 20.
There seems to be this bubble of thinking on HN that hard labor jobs don't pay well. The reality is they pay more than your average IT Support job. They are in demand because they can't find people willing to do the work. Another example is electricians. Some electrician companies are so desperate for skilled electricians that they are paying their retirees to come out of retirement and still allowing them to keep pension benefits. Another one is plumbing, etc.