Measure the distance between the door and the ground and sketch out a plan for the steps. Make sure the planned stairs are all the same height and depth, and that the stair height and width conform to local building codes. Use these measurements to determine the length of the stringers (supports) and the distance from the house to the base of the stringers. If a ledger board isn't present, install one and measure from the front of the board.
For greatest comfort, design the stairs with a 6" to 7" rise (height) and a 10" to 16" run (depth).
Measure from the exterior wall to determine where the bottom of the stringers will rest. Dig holes at these points for the concrete footings that will support the bottoms of the stringers. Make sure to dig the holes to the depth specified by local building codes.
Cut cardboard concrete forms to the proper height and slip them into the holes. Make sure the tops of the forms are level. Use a hoe to mix concrete in a wheelbarrow, according to the package instructions; the concrete should be the consistency of oatmeal. Pour the concrete into the forms and smooth with a trowel.
Measure the distance between the concrete footers and cut a pressure-treated 2" x 4" to fit snugly in between them. Measure and cut a second pressure-treated 2" x 4" to fit behind the footers. These boards will support the stringers.
Measure and cut the top and bottom posts from 4x4s. The height of the bottom posts should be the desired post height plus the depth of the concrete footing. Sink the bottom posts into the wet concrete, making sure they are plumb and remain in position while the concrete dries.
Use a carpenter's square to measure and mark the cut lines for the stringers based on the rise and run in the design (Image 1). Use a circular saw to cut along the lines, stopping just short of the end of the lines. Finish the cuts with a jigsaw for better control and cleaner results (Image 2).
Once the stringers are cut out, measure the thickness of the stair treads. Cut this amount from the bottom of the stringers so that all of the stairs end up the same height.
Once the concrete is dry, position the side stringers. Use galvanized lag bolts to attach the stringers to the bottom posts; use deck screws to attach them to the ledger and the 2x4s resting on the ground.
Use deck screws to attach the middle stringers to the ledger and the bottom 2x4s. Use lag bolts to attach the top posts to the side stringers.
Measure and cut the vertical rails from 1x2s and install them using galvanized deck screws. Make sure to follow local building codes for the distance needed between the vertical rails; most communities require 6" or more between rails for safety reasons.