Fixed ladder, temporary ladders, stairs and manlifts are all potentially safe methods of accessing a roof.  A job hazard analysis should be performed to ensure the access can be done in a safe manner.  If near the edge, protecting access points with additional guardrail around the access point to protect the worker once on the roof should also be considered.  Depending on the height of a fixed ladder it may require additional fall protection. Ensure temporary ladders are used correctly and extend above the roof level and are not near a roof corner.  When using a man lift to access a roof ensure it can extend to a safe place to access the roof before exiting.