Bill,
Yes it is safe. But, there are some guidelines to be aware of.
Once on the roof the use of carpet, reversed, or a blanket or toweling to
protect the skin from whatever is on your shoes is recommended.
Getting on the roof can be done a number of ways. One of the simpler ways uses
the patio awning case as a step over point from an 8' step ladder. Another is to
put padding on an extension ladder were it contacts the awning case. Several
other folks on the list have other ideas as well.
Charlie