The materials you'll need for this project include a footboard with front side upholstered (refer to How To Make a Two-Dimensional Upholstered Headboard and Upholstering a Curved, Diamond Tufted Headboard to get instructions).
Start with a full sheet of 3/4”-thick plywood. Have the hardware store cut it two inches wider than the width of your bed. The height of the headboard can be adjusted by cutting legs to size. Be sure to save any plywood scraps for later use. If you’re upholstering an organically-shaped headboard, freehand the shape on a large piece of paper. Then trace the paper pattern onto the plywood. If the shape is symmetrical, draw half of the shape on paper and trace it onto the plywood and then flip the paper pattern over to trace the other half.
To make rounded corners, first determine the radius of the curve. Hammer a nail into the plywood the same distance from the edge as the radius. Attach a string of the same length to the nail on one end and a pencil on the other. With the string taught, use the pencil to mark the curve.
To conceal hardware, place bolts in between the two layers of plywood so the threaded ends stick out of the backside. Before you finish the backside of the footboard, upholster the front side. Refer to Upholstering a Curved, Diamond Tufted Headboard for instructions on completing various types of upholstery constructions. Staple webbing to the frame of the footboard and stretch to the opposite side with a webbing stretcher. When the webbing is to the desired tightness, staple and cut off the excess 2” beyond the staples. Fold back the 2” excess and staple again. Continue stapling strips of webbing vertically and horizontally across the frame. Space strips 4” to 6” apart and basket weave them as you go.
Welt cord is optional, but if you plan on attaching it, follow the instructions for making cording from Make a Two-Dimensional Upholstered Headboard. Use your index finger and thumb to line up the welt cord with the wooden edge of the footboard and staple through the tail of the welt cord into the frame of the footboard. Start and stop the ends at the bottom middle of the footboard, leaving an inch of excess on either end. When the cording is stapled all the way around, open up the ends and cut out the excess cording so they meet.
Neatly finish the fabric at the connection in the welt cord by laying one fabric end out straight and folding the other end under and around the cording. Secure the cording in place by stapling to the footboard.
Push the foot of the Pli-Grip into the welt cord and staple so one prong goes through the hole of every foot. The teeth should close down towards the outside of the footboard. At corners, cut the Pli-Grip, and begin the next side with a new piece. When it’s attached all the way around, push the teeth down firmly.
Cut a piece of fabric large enough to cover the backside of the footboard plus a few extra inches. Be conscious of pattern placement and direction as you cut the fabric. Smooth the fabric over one side and mark the outside edge of the Pli-Grip with chalk.
Use the flat end of the regulator to tuck the fabric into the teeth of the Pli-Grip. When you’ve secured the fabric on one side, smooth the fabric to the opposite side and repeat the steps to cut off the excess and tuck the fabric into the Pli-Grip. Keep working until the fabric is attached around the perimeter of the footboard.