Set up your DJ gear on a table, pack it snugly together and measure the area it takes up; remember to leave 20 mm borders around all the edges to accommodate the foam padding. Cut two large hardwood sheets with a band saw to match the surface area taken up by your equipment. The planks should reflect the length and height of the sides of your setup.
Place your setup on one of the sheets to ensure the correct size; all your equipment should fit on the board without any overhang or protruding parts. Pay particular attention to the planks that will make up the front and rear edges; check to ensure they are tall enough. Cut the planks in half lengthwise with a band saw. If they previously measured 4 feet by 6 inches, they should now measure 4 feet by 3 inches, and you will have four instead of two. Repeat with the planks for the sides.
Screw the side planks to each of the sheets with wood screws and a screwdriver. You should now have two identical "trays," each one consisting of a large sheet with the same area as your equipment and a four squat "walls" around it. Stick high-density insulation foam to the insides of the trays using a glue gun. Cover all surfaces with foam, as if carpeting and wallpapering a room.
Place one tray face down on top of the other to create your case. Screw breakaway case hinges along one edge, and fit heavy-duty clasps around the other three sides. Attach heavy-duty carrying handles on the opposite edge to the hinges -- the side closest to you when you're DJing.
Set up your equipment inside the lower tray, and you're ready to go.