When building stairs for your deck you will also be expected to follow the IRC building requirements.  These requirements are strictly enforced by buildign inspectors.  The minimum width for stairs is 36”, but we recommend using 48” stairs wherever possible.  The maximum riser height is 7-3/4” and the minimum rise is 6”.  The minimum stair tread should be measured at no less than 10”.  The tread width and riser height shall not exceed the smallest by more than 3/8”.  This means you will have to plan ahead to make sure each and every one of your stairs measurements are the same.  In other words plan ahead so you aren’t left with a really tall or short last step because you will fail the inspection.  Open risers are permitted by code with a catch because they may not be large enough to permit the passage of a 4” sphere the same as rail infill rules.  In most cases it looks nicer and is just plain easier to close the risers.    You must maintain a minimum 6'-8" headroom clearance and provide stairway illumination.  Stair stringers should be cut from 2x12 pressure treated lumber and spaced no greater than 16" O.C.  Always verify stringer spacing requirements when using composite materials for stair treads.