Place a 90-degree-angle PVC fitting onto either end of a 48-by-1-inch PVC pipe to create the crossbar. Adjust the angle of the fittings so they both point the same way. To attach the pieces together, slide the pipes into the joints on the fittings.
Insert a 48-by-1-inch pipe into each of the 90-degree-angle fittings.
Place a 90-degree four-way PVC T on the end of each 48-inch pipe. When you put the Ts on, position them so the sides with no joints point downward and to the outside of the structure.
Insert a 48-by-1-inch pipe into the four-way PVC T joints so the new pipe runs parallel to the 48-inch pipe.
Insert an 18-by-1-inch PVC pipe into each of the four open joints in the Ts.
Insert the ends of the 18-inch pipes into one of four 90-degree-angle joints. Adjust the joints so they point the same direction as the 90-degree-angle PVC fittings.
Add a 4-by-1-inch PVC pipe on the open end of each 90-degree-angle joints. Place a PVC cap on the end of each 4-inch pipe to finish the frame.