Building a set of wood stairs is not nearly as hard as you may think. With some basic wood tools and a bit of algebra you can easily build your own. Of course this can get a bit tricky for stairs with several landings but the method is still the same. This article will cover the steps for building a straight set of stairs. Chances are if you are reading this then you are still learning and won't be taking on a complex stair anyway. Now, we will assume that it is from a deck to a concrete pad. The deck is going to be 48" wide and at eye level from the ground.

Tools you will need: Circular saw ;
Framing square; Hand saw; Carpenters pencil; Measuring tape; 4' Level; Masking tape

You will also need: 3 @ 10' / 2" x 12" boards - Choose the best only, make sure they are straight with no check (cracks). Very Important!
2 @ 8' / 2" x 4" boards
8 @ 8' / 2" x 6" boards - Once again choose the good ones. These are going to be the steps so...
1 @ 45" / 2" x 6" boards
1 sheet of plywood @ 1/2" / 8" x 48"
Of course, 3-1/2" framing nails and deck screws or nails for the steps.

Find the overall rise: We want to know the exact vertical distance from the top of the concrete pad to the top of the deck. Take one of the 8' 2x4's and rest one end on the deck and hold the other over the pad, Place the level on the 2x4 and level the board. Then simply measure from the bottom of the 2x4 to the pad. Lets say it is 64". This is the overall rise.
Now determine the overall run: Before we can do this we have to determine how many steps we need.
So first..: Take the overall rise, 64", and divide it by 7.25", which is the typical height of 1 riser (step). This gives us 8.83, which rounds up to 9, So we will go with 9 risers.
Important: There is always 1 less tread then risers. Whether you go up or down the last step is onto the deck or the pad. So 1 less tread.
Now we take 10.5", the width of a typical step, and multiply it by 8. This gives us 84". This is the overall run.
While we are doing the math we need to figure out the exact rise of each step. We simply take the overall rise of 64" and divide it by 9 and we get 7.111" or 7-1/8", or close enough to it. So each riser will be 7-1/8".
Time for some layout: First thing. Grab your framing square. The long leg is the tread (step) leg and the short leg is the riser leg. Also, use the numbers on the outside of the square only.
Take some masking tape and wrap a piece around the framing square to establish you rise and run. Mark 10.5" on the outside of the long leg and 7-1/8" on the outside of the short leg.
Layout one of the 2x12's on your saw horses or work bench. WIth the long leg of your framing square towards the end of the board start to line up the tape marks to the edge of the board facing you. Once you have the square in position mark the outside edge of it with your pencil.
Continue to do this until you have the required number of steps, 8 in this case. This first riser is always shorter by the thickness of the steps, for us that is 1.5". This makes the first riser 5-5/8".
Cut 'em out: Now use you circular saw to cut out the stringers (technical name for 2x12 with stair marks on it) being sure to cut on the waste side of the line. When you cut into the corner with a circular saw the blade misses some of the wood on the bottom side of the board. This is fine, simply cut up to the line and stop, then finish the cut with your hand saw.
Now use the first stringer as a template for the other two. Lay the stringer onto the 2x12's and trace around it. Then cut out the other stringers the same as the first.
Reinforce the stringers: Align one of the 8' 2x4's along the bottom edge of the string and mark it to fit the profile of the ends of the stringers. Cut the 2x4 and secure it to the bottom edge of the stringer. Repeat this for one other stringer. These help to strengthen the stringers and reduce "bounce" in the stairs. Use the framing nails to secure them.
Assemble the stairs: The plywood is used to attach the stairs to the deck. Secure the sheet of plywood to the top end of the stringers. The two outside stringers are nailed flush with the edge of the plywood while the third stringer is centered on the sheet. Simply nail through the plywood into the face of the stringers using framing nails. 4 into each stringer will be enough.
Now take the 45" 2x6 and nail it in between the bottom of the outside stringers. The 2x6 will fit into the notch cut into the center stringer. This provides the right spacing for the bottom of the stairs and secures them to the pad.
Attach them to the deck: Move the stairs into their final position. make sure they are level across the stringers and that the risers are plumb. When the stairs are positioned correctly nail through the plywood into the side of the deck. Use some 3" concrete nails to secure the 2x6 spacer to the concrete pad.
Install the treads: Cut the 8 - 8' 2x6's in half, be sure to cut them square. Starting at the bottom of the stairs, start placing the 2x6 stair treads. Simply center them on the stringers and use some 3"deck nails to attach them. You can also use an exterior adhesive to assure that they don't move.
Continue to work your way up the stairs until you reach the top. You are done... well, almost Railings. You need to install a railing to keep people from falling off.

About The Author: Dave Markel is the author of "The All Wood Working Journal". He has helped hundreds of individuals improve their wood working skills. Visit his site at http://all-wood-working-plans.com.