You can stand safely on the roof, but you need to stay only on the ribs. The ribs can be identified by the row of rivets. There is one row of rivets from front to back on each side of the roof. There is no rib there.
A/C units are heavy and awkward to move around. You will need at least two people on the roof to lift it off. Getting it removed depends on how it is attached. Some use 4 bolts and they can be removed quickly. My old unit had around 40 screws and rivets attaching it and the drain pan to the roof.
WBCCI President 2016-2017