Cut 1 3 frame parts to match the plywood dimensions then glue and nail them together with 1 1 2 in.
Adding a drawer under a table.
Narrower and 1 4 in.
Measure the cavity under the cabinet and cut a piece of 1 4 in.
Shallower than those dimensions.
All you need to do is make 45 cuts into two pieces of wood then attach them together at a 90 angle.
Screw this piece vertically onto the side of the drawer and let it hang down from your desk top.
Measure across the face of the drawer from side to side and mark the center of the face.
Add the drawer bottom.
Build the drawer frame.
Place the drawer on the countertop or a table.