The first two are most difficult (you have no where to stand and work at that point), but after that it is easy. (Assuming your roofing material is the same gauge as mine was.)
We would lift a panel to the edge (eve) then slide it up on the main part of the roof. There was never any threat of kinking, and if you worry about finish you can drop some duct tape on the edge you are dragging along, I found it unnecessary. With 19' pieces you may find a helper below pushing may be useful, mine were about 17' and I did about half the roof single handed.