I had my hip replace in my late thirties in 1988. I was very active after the surgery. However, I think doing roofing could be very dangerous.
The squatting/kneeling position is a no-no. You can't be twisting your leg around because you would likely have a dislocation. One mistake- not paying attention to what your lower body is doing- and you could dislocate and probably fall off the roof. I've dislocated twice in the hospital and it is excruciatingly painful.
I wouldn't recommend roofing as I wouldn't recommend laying carpet.