With a stair landing that is reasonably easy to modify you might consider creating extra storage space. Assuming there is an unused “dead space” you have the opportunity to install a stair trap which will allow you to create an area roughly three by four feet deep into which shelf racks could be installed. If the shelf racks are self-assembly they can be adjusted to suit your needs.

To begin, remove the floor and sub-floor from the landing. Be careful about pipes or electrical wiring possibly running alongside the floor joists. Remove the top two treads and stair risers.

Nail the ledgers to the floor joists on either side of the opening, allowing room for the thickness of the door framing. Cut the subfloor plywood to size and fasten the side frame pieces to the lower edges of the panel. Attach the frame pieces to the panel at each end.

Cut the stringer pieces to size, attach them to the lower front edge of the subfloor panel. Fasten the remaining frame member across the bottom of the subfloor at the point where the stringers end. Cut risers and treads to size, cut the grip and attach it to the face of the front riser. Install the finish flooring in place atop the subfloor.

Place the assembled unit in position. Fasten strap hinges to wall and flooring.
Open the door; fasten the angle bracket to the door frame. Attach the gas struts and establish where to attach the remaining set of support brackets. Finish the floor material to match the existing floor.