Arrange and secure a frame of joists to set the floor on, setting the beams about 4 feet apart. The floor will measure 40 feet by 20 feet. A simple lattice pattern is effective.
Lay the floor flat on the beams and secure it with screws drilled through the flooring into the beams. Fasten every 6 to 8 feet. The floor and walls should be made of hardwood planking or treated particle board. Some courts use glass, but glass can be more difficult to work with.
Erect vertical joists along the four edges of the floor, securing them to the floor joists with at least four screws at each junction. The vertical joists should extend at least 10 feet in the air.
Brace the vertical joists with horizontal girders at 5 and 10 feet off the ground, and then brace those girders with diagonal support beams that slant outward from the structure to the ground for support.
Attach the walls from within, securing them firmly with screws to every joist.
Attach the roof and secure it to the walls with screws through the top and into the walls every 4 feet.
Measure 18 inches in from each wall and mark the spot in each of the four corners that is 18 inches from both adjacent walls. Each spot will be 25.46 inches from the corner.
Connect the four points with tape, stuck to the floor, marking a playing area 40 feet by 20 feet, 18 inches from the walls.
Measure 20 feet from either end-line to the center of the court, and tape a line across the court, dividing the floor into two 20x20 squares.
Measure and mark two more crossing lines parallel to the center line, on either side of the center line, 5 feet away from it.
Measure points along the center line and along the parallel line closest to the front wall. These points should be 18 inches and 36 inches from the sidelines. Tape between these points, a total of four dividing lines, each 5 feet long: two 18 inches from the sideline and two 36 inches from the sideline.