Sketch a guitar case design, then cut a yellow-green canvas material and a blue denim material in alignment with a guitar shape using a tape measure, tailor's chalk and a pair of scissors. Cut four pieces of material, two from each material and two more cuttings from the soft padding sponge, one for each side.
Measure two pieces of canvas, each measuring 1 foot by 1 foot, using the remaining canvas materials. Fold the three sides of the first material, 1 inch from the edges and sew it on the second canvas to make a flexible pocket, then sew the joined canvas piece to the larger part of the canvas that has the guitar shape. Add zippers to make a two-in-one pocket. Repeat the procedure with the denim material.
Place the canvas material on a flat surface and put the soft padding sponge on the material, then add the denim material in alignment with the shape of the guitar. Sew the edges of the combined materials all together. Repeat the same procedure with the remaining materials to make two, equal-size guitar case materials.
Join the backside of the two complete parts by sewing from the top half to the bottom half. Cut 4 inches by 3 feet of the materials for the straps using part of the canvas materials, place it in the soft padding sponge, then enclose it by folding the width in half. Sew the edges and the center line to make a long strap.
Sew the straps to measure 1½ feet on both sides of the pockets, then turn the material inside out and repeat the same for the denim material. Fix a two-sided, 4-foot length zipper to the remaining opening of the guitar case so that it can open both ways. Place your guitar inside, close the zipper, turn it inside out and close the zipper again to confirm its compatibility.