Cut eight scaffolding poles to size using a hack saw. You need four poles to be 30-inches long for the legs; two poles to be 72-inches for leg supports, and two middle support poles at 36-inches.
Lay out two leg poles, perpendicular to each other. Space them 72-inches apart or the width of the stage platform.
Place one leg support in the middle of the two legs and weld the ends of the support beam to the legs. This create an H-frame. Repeat Step 2 and Step 3 for the other two legs.
Form an X under the stage using the middle support poles. Weld one end of a support beam to a right corner leg and the other end to the opposite left corner leg. Repeat this step for the other support pole until you have two poles that cross each other.
Sand the plywood. Paint, polish or varnish the surface of the plywood to give a professional appearance. Use a dark color such as black or gray.
Cut a hole in all four corners of the plywood. The hole should be the same diameter of the scaffolding poles.
Lay the plywood runway over the frame you built. Push the four corners with pre-cut holes down over the scaffolding poles. These holes keep the catwalk platform in place as the models walk back and forth.
Line up two or more completed runways so they form a T-shape. Attach the legs of the catwalk with metal clasps.