If you've had little experience in landscape construction projects, it may be well worth your time to have a professional contractor design the steps for you. (Any retaining wall over 4 feet in height should be professionally engineered to ensure structural reliability.) You could also find a good how-to book on landscape construction that will provide you detailed instructions. Here are some points to keep in mind. Check local codes and ordinances for regulations on stair dimensions, railing requirements, and other parameters. Chose a durable material that will blend well with the retaining wall and your home. Consider the steepness of the stairs. Treads should be a minimum of 12 inches deep. The shorter the rise (the distance stepped up between each step), the wider the tread should be. Typical combinations include a 6-inch riser with a 14-inch tread, a 5-inch riser with a 16-inch tread, and a 4-inch riser with an 18-inch tread. Break up long, steep slopes by curving the flight of stairs or by shortening the spans with landings.