There are all kinds of reasons for an access door. It might be for a water heater, storage, access to an open space in the wall below stairs, or any number of spaces where you can't install a factory-made door. Simple hardwood plywood works as a panel door, but it can be boring. Dress it up with a Shaker or beadboard design for a decorative appearance. It's light, functional and trendy.
Measure the width and length of the opening where you wish to place the panel door. Add 1 1/2 inch to the measurements. This allows the door to overlap the opening by 3/4 inch on all four sides.
Cut a piece of 1/4-inch-thick hardwood plywood to the measurements using a table saw. Lower the blade on the table saw to 1/8 inch from the tip of the highest tooth, to the point where the blade enters the table.
Divide the panel into 2-inch-wide sections, parallel with the grain from left to right. Mark them with a pencil. Set the fence on the table saw to align with the first mark. Turn on the saw and push the panel over the blade, face down, to create a kerf, or line across the face of the panel. Reset the fence for the next line, cut it and repeat until you've cut kerfs across the panel. This is a decorative beadboard pattern.
Measure the length of the panel. Cut one piece of 3/4-by-2-inch hardwood for each side of the panel using a miter saw. Add glue to the back of each piece and nail it flush to the sides of the panel penetrating up through the plywood from the bottom, using a pin nailer and 1-inch pin nails.
Measure the distance between the two side pieces. Cut two more pieces to fit between the two side pieces. Add glue, place them between the two side pieces, flush at the top and bottom, and nail them on from the bottom.
Sand the door by hand using 100-grit sandpaper. Round and blunt all the corners and edges. Finish with stain and lacquer, varnish or paint. Screw the door to the framing around the opening using your choice of hinges.