Lay pressure-treated 2x4 boards around the perimeter of the porch. Use a framing square to make sure the sill plate is square. Fasten the sill plate to the concrete floor using lag bolts and concrete anchors (Image 1). Attach a layer of untreated wood on top of the sill plate to provide a base for interior trim work. Use a reciprocating saw or a handsaw to remove the sill plate from door opening.
Stand a stud on top of the sill plate against the wall, check for plumb and temporarily fasten it in place. Place a board for the top plate against the ceiling, using the upright stud to support one end and another stud to support the other. Nail the top plate to the ceiling. Repeat this process around the perimeter of the porch.
Check the width of the screen before installing the studs. Most screens come in 3' widths, so space the wall studs on 3' centers. For door frames, place two studs on each side of the door opening. One will be used for attaching the screen and the other will be used for the door hinges.
Use a level and a chalk line to mark a line on the wall studs 32" from the floor. Cut 2x4 boards to length and install them horizontally between the studs to create the top rail. Cut balusters from 2x2 boards to fit between the top rail and the sill plate. Position the balusters so they're evenly spaced and flush with the outside wall. Secure them with finish nails.
Prime and paint the porch frame and screen door. When priming the screen door, use masking tape to prevent primer from getting on the screen.
Cut the screening to length and staple one side of the screen to the wall studs (Image 1). Stretch the material taut and staple it to the other stud. To cover the seams, cut lath to length, prime and paint the pieces and nail into place. Follow this order: top horizontal pieces first, followed by the bottom and balusters, then the vertical pieces (Image 2).
Place a scrap piece of lath under the door so there is a 1/4" gap between the slab and the bottom of the door. Attach the door to the wall stud with hinges. Install a rubber sweep on the bottom of the door to prevent insects from entering the porch (Image 1). Install any remaining hooks, latches, springs and hardware.