Bad on the back and knees, high risk of falling, strokes from heat for older roofers, and the careless ones start throwing hammers around. (I'm not a roofer, but used to be a jack of all trades that sometimes did roofing alongside actual roofers.)
Yes as other have stated the profession is rather hard on your body. I suffered some serious back problems as a result of the manual labor and decided to peruse my interests in engineering instead.
