These will be in the air above ground following the contour? Or are you building them on the ground?
I would go the ground route. In levels you can build stairs with pressure treated landscape timbers. Just keep them at the 6x6 stair height and work your way up from the bottom. Some crushed stone underneath is good for drainage and to get rid of the layer of topsoil. Looks better than a set of stairs outside.
You can also use block, stone or composite materials. Check out your local building supply company, or even a landscape supply company would be better. There are plenty of ideas out there, just Google it.
If you have specific questions when you start, ask away in the landscape threads.