Rocks are great materials for integrating your garden stairs into the surrounding landscape elements. Though it is easier for some to negotiate a ramp than stairs, sometimes sloped gardens don't allow for ramps due to space, degree of slope or aesthetics. Stairs can be complicated to build, but if you are landscaping in an area that has lots of natural rocks, it can be a great use of your resources. Ultimately, rocks as garden stairs can make for a lovely addition to a garden.
Find rocks that aren't factory cut. This can be a bit challenging, but will give your one-of-a-kind set of stairs their sculptural value. Choose rocks that are as flat as you can find, and about as wide as the adjacent path leading up to them. It is good if you can find ones that are also at least a foot deep, but preferably more.
Dig a flat area out of the slope in which to place your first step, starting at the bottom of your staircase. Dig this area to fit the contour of the base rock, which should be the largest.
Check the level of the ground on which you will place the base rock--side to side and front to back. If it is leaning immensely one way or the other, scrape it as flat as possible with a short section of 2-by-4.
Place your base rock and set the level on it to see if it needs more adjusting. Working with uncut rocks, your steps aren't going to be as pristinely level as if you were building with cut granite slabs or concrete steps, but you can get them relatively flat. Your rock may need a little more dirt added under one of its sides to bring it more level.
Dig the next flat area out of the slope for the next rock stair, above the base rock. You will need to dig into the slope far enough so that the next rock fits behind the base rock, while overlapping it by at least an inch to cover the back of the step below it.
Repeat the leveling and placing for the second rock, and continue for as many rock steps as you need to complete your rock garden stairs. You may wish to add some plants to further integrate the stairs into your garden. As Nicholas Klise writes in "Rock Garden Design and Construction," garden steps can be discreetly planted with tiny perennials or mosses as long as the result does not impede walking. These plants must be very low and their growth controlled so they don't obstruct or visually interrupt the movement of walking up the stairs.