To build porch steps, first calculate the rise and run of the proposed stairs. With those measurements in mind, cut and mount the stringers. Once secure, place the treads and risers.
To calculate the rise of the stairs, place a straight board on the top of the porch, allowing it to hang slightly over the edge. Measure the distance from that board to the ground; this is the rise of the stairs. Take that number, and divide it by seven, which is the typical rise of each step. If a decimal is produced, round down to the nearest whole number to determine the number of steps needed.
Divide the measured rise by the number of steps to determine the actual rise for individual steps. To find the stairs' run, measure the horizontal distance to be covered by the stairs, and multiply it by the number of steps needed.
Cut four stringers according to the calculated rise and run. Attach them to the porch by securing them onto the rim joist or placing them just under the frame. With the stringers in place, cut the risers according to the width and length of the stringers, and secure them with deck screws. If adding a handrail, place the 4-foot-by-4-foot posts before laying the treads. Cut the treads to the appropriate length, and screw them into the top of the stringers, leaving 1/8 to 1/4-inch of space between them on each step.