Measure your keyboard's length and side width. Cut out pieces of canvas to form the front and backside of your case. Make your pieces at least four to seven inches larger all the way around to account for stitching seams and the height of the keyboard. Add seven to 10 inches on the back piece to form a flap to fold over the top. Measure how long the handles need to be to carry the case, and cut out four handle strips.
Pin two handle pieces together twice with the outsides facing in to form two handles. Use a sewing machine with a canvas needle to sew around the outside edge of the pieces twice for durability. Sew around the edges of the two handle pieces, leaving an opening at one end. Turn the handles right side out through the opening, and then sew the opening shut by hand. Sew the handles to each side of the bag by sewing a square at each handle end and then sewing an "X" through the square to reinforce the handles.
You can form a 1/4-inch folded-over seam on the flap or just sew around the flap edges to finish off the material.
Measure and cut out two pieces of padding that are slightly smaller than the sides of your case. Do not line the flap with padding, as this makes it too bulky. Use a glue gun to glue these pieces on each side of the case with the case inside out. Wait for the glue to dry. Turn the case right side out.
Measure where you want the case closures to be. If your case is longer than 2 feet, you should at least use six to 10 closures to keep your keyboard secure. Peel the backing off the Velcro tape and press each sticky side down into place on the underside of the flap and at the top on the front of the case.
Glue four plastic 1-inch corner pieces into place on the bottom of your bag. Wait for the glue to dry. You can use larger corners for protection against bumps, especially if the carrying case is longer than 24 inches.