Use pressure treated wood and galvanized roofing nails to hold up against the outside elements. Under the Americans With Disabilities Act (ADA) guidelines, a landing of this kind should be at least 5 ft x 5 ft. This is so that someone in a wheelchair could turn completely around in a circle without getting stuck. Using a chop saw, cut frame pieces to size.
Using a framing nailer, assemble each of the pieces of wood to create a frame (Image 1). For additional support and stability, cut and attach cross joists to the inside of the frame every 16 inches (Image 2).
Once the deck frame is built, place it flush along the edge of the doorway and flush on the concrete. Check to make sure it is level both horizontally and vertically (Image 1). Add a few shims made from pressure treated wood where needed to level it up (Image 2) and to provide much needed ventilation.
To create the ramp, measure from the distance from the top of the landing to concrete base. Then cut three boards using this measurement on one end and angling the cut down to a point (Image 1), creating ramp supports. Next, fasten the three ramp supports to the side of landing frame (Image 2).
To make the ramp more stable, use wood cross braces between each of the three ramp supports. Secure these to the concrete. Drill two pilot holes into each brace using a masonry bit (Image 1) and fasten using concrete anchors or screws (Image 2). Then fasten each of the braces to the ramp supports (Image 3).
Add the deck planks across the ramp and the landing frame. Start by placing a full board where the angle of the ramp changes (Image 1). Be sure to orient the boards so that they are crossways or perpendicular to the ramp. Placing the decking this way ensures that a wheelchair will not get its wheels stuck in the seams between the decking boards. Secure each board working out as you go (Image 2).