Draw a large, fat X on plywood. The letter should be at least 24 inches by 36 inches. Cut out the X using a jigsaw.
Attach a leg bracket centered on each leg of the ottoman. Use the bracket as a template for the attachment holes. Mark the holes. Drill through the plywood. Bolt the brackets to the plywood using lag bolts, washers and nuts. Tighten the brackets with a wrench.
Spray the top of the X with spray adhesive for foam. Press a piece of 6-inch thick foam over the X. Trim the foam around the perimeter of the plywood using an electric carving knife.
Place a piece of quilt batting on the table. Turn the foam-covered X upside down and centered on the batting. Wrap the batting to the back underside of the wood. Staple the batting to the underside of the wood. Cut the batting so that you can cover the sides of the letter X. There will be gaps along the sides of the X that the batting doesn't cover. Cut batting pieces to fit the gaps. Hand sew the batting together until all of the sides are covered and smooth.
Place the decorator fabric face down on the table. Place the ottoman face down over the fabric. Trace around the outside edge of the ottoman, adding 1/2 inch for seams. Cut out the top cover with scissors.
Measure around the perimeter of the X from corner to corner. There are 12 outside corners on the X shape. The first outside corner is at the top left. Call that corner 1. The second outside corner is horizontal and to the right of corner 1. The horizontal line from corner 1 to corner 2 form the top of the top left X leg. Measure from corner 1 to corner 2. Add 1 inch for seams. Use this measurement as the length of the piece. Cut decor fabric to this measurement and 8 inches in width. Place a piece of tape on the piece of fabric labeled 1 and 2. Measure from corner 2 to corner 3. Corner 3 is a downward slant to the top center of the X shape. Add 1-inch for seams. Cut your second piece. Label. Continue until you have 12 labeled pieces. Corner 4 is the top right corner of the top right leg of the X shape. As you can see you are measuring around the outside of the X shape like an outline using the corners as seams.
Sew the side pieces together in order. All of the pieces are 8 inches tall. Piece 1 and 2 will join with 2 and 3, which will join with 3 and 4, connected to 4 and 5, attached to 5 and 6 all the way until you reach 12 and 1 which, will attach to 1 and 2, forming a complete circle. Place each piece of fabric right sides together and sew a 1/2-inch seam.
Place the cover right side up with corner 1 at the top left. Position the side cover face sides together with corner 1 matching up with the top cover at corner 1. Pin the seam. Sew a 1/2-inch seam all around making sure all of your corners match. Cut the seam allowance at a 45-degree angle at each corner to reduce bulk. Do not cut the seams. Turn the cover right side out and fit it onto the ottoman.
Pull the cover snug. Turn the ottoman upside down on the table. Stretch the fabric to the back underside of the top leg of the ottoman. Staple 2 inches from the edge of the wood on the underside of the ottoman. Go to the bottom right leg. Stretch the fabric taut and staple. Go to the top right leg. Stretch and staple. Go to the bottom left leg and stretch and staple. Continue working around the ottoman from side to side and top to bottom to evenly stretch and staple the cover to the underside. Staple every inch. Trim off the excess fabric. Attach the legs by screwing them into the brackets.