We use the sharkskin now on roofs, other than needing plastic cap nails, it's good stuff. Never walk on it if there is even a drop of water on it, unless you like the 10-yard freestyle bobsled! Not sure if it's worth the extra cost, surely not needed for this project. A well-installed steel roof can last up to 100 years or more if it's maintained. I have snow dogs on my garage so the door doesn't get blocked by falling snow and ice. Cost is always a factor, though.