You don't have to necessarily rely on contractors or other "professionals" to build a trusty set of deck steps. By reading/following these rules, you'll find that the steps can be built either before or after the deck boards are in place.
Measure height of deck.
Divide height of deck by 6 or 7. (Six or seven inches is the normal riser height.) This tells you the number of steps you need from the ground to the top of the deck.
Calculate the tread (the width of the step from front to back), or T. Twice the riser height (or R) plus the tread width should be between 24 inches and 26 inches. Or, (2 x R) + T = 24 to 26. So, for a riser that is 6 inches tall, the tread should measure between 12 inches and 14 inches. (Some leeway is allowed for comfort when using the steps.)
Pour foundation and add a kicker plate, if wanted. (A kicker plate is a board attached to the foundation with bolts or concrete nails; the bottom of the stairs can be attached to it.)
Transfer step measurements, as determined by calculations in Section 1, onto a 2-by-12 treated board that will be your first stringer. (A stringer is a board that has the pattern cut into it - it helps you form your stair-size calculations.) First mark the height dimension of a step onto the short arm of a framing square; place the framing square to the board with this mark at the outside edge of the board. Then hold the square in place and slide it up and down until the width dimension on long arm of square is on edge of board.
Trace around outside edge of framing square. (Your tracings will look like a V.)
Continue marking treads. (Now your board will look like VVV.)
Subtract the tread's thickness from the bottom of the stringer and notch out the bottom to fit around the kicker plate.
Cut along the trace lines with a circular saw or handsaw.
Check the alignment with the deck, then trace and cut a second stringer using the first as your pattern.
Attach the stops of the stringers to exposed joists with bolts or to end or rim joists with joist anchors or angle brackets.
Attach the bottom of the stringers to the base or kicker plate with angle irons with lag screws.
Cut risers and treads to the desired width of your stairway, leaving 3/4-inch overhang on each side.
Screw or nail risers in place, then add treads. Fasten bottom edges of risers to backs of treads.
If you end up with a fraction when dividing the height of the deck by the riser height, round to the whole number and divide into the height of the deck to determine the height of each step. Steps should be at least 4 feet wide to be comfortable for one person to use (service stairs can be as narrow as 2 feet across). Wear safety glasses.
Remember that the true height of R is the distance from the top of one tread to the top of the next tread; keep the dimensions of your lumber in mind. Requirements for stairs are: 7.75 inch risers maximum. Landing or tread are to be a minimum of 10 inches deep. The width of the stairs are to be 36 inches minimum. With more than three treads [stairs] a hand rail is required. Be sure to check local codes for specifics in your area before you begin building.