Lay pressure-treated 2×4 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.