If your residential roof is installed over a solid substrate, you should be able to walk on your roof without damage; just avoid stepping on the ribs or the ridgecap. However, it is much easier to lose your footing on a metal roof due to moisture or loose debris. If your roof is commercial/industrial and installed over open purlins, walking on your roof is not recommended, so consult your roofing installer before you do. Since a metal roof requires virtually no maintenance, there should be no reason to be on your roof.
