Draw rectangle on the plywood board. This rectangle will be the base of the cage. Cut it out with a coping saw and drill a hole into each corner, the same diameter as that of the wooden dowels. These holes should be at least ¼ of an inch away from the apex of the corner. Cut the wooden dowels to a length equal to the height of your cage and then dab glue in each of the four holes. Insert the wooden dowels into each of the holes and hold until the glue dries.
Drill more small holes, at least ¼ inch from the edge of the rectangle, around the edge of the plywood base. Drill one hole for each bar on your cage, 1/4 inch apart, these holes need only be large enough for a cable tie to fit through. The holes need to be this close together to prevent material falling out of the desk tidy.
Measure the distance between two adjacent dowels and add an inch. Cut a piece of wooden dowel to this length and hold it up to the two dowels so that half an inch protrudes on each side and half an inch of the existing dowels are above it. Wrap a cable tie around one end, lashing the dowel to the existing vertical dowel and pull it tight. Repeat this at the other end of the dowel and the horizontal dowel should hold tight in place.
Repeat this with the other three sides of the rectangle. When two horizontal dowels meet at a junction, wrap the cable tie around all three dowels and pull tight. This way the different dowels are supporting one another. Continue until you have a set of horizontal bars around the top of the structure.
Feed a cable ties through one of the small holes in the base of the cage. Wrap the tie around the horizontal bar directly above the hole and pull tight. Continue until all the holes have a cable tie pulled tight through them. The solid plywood base and the amount of cable ties so close together will make the desk tidy secure and ensure that nothing can fall through the gaps in the cage. Trim the excess cable tie ends.