For complicated shapes like like the example above, your best bet is to cut it from .060" or .080" sheet stock, depending on the size you need. For example, for 2x3 rectangular tubing, use .080" sheet. Glue two pieces of plastic together face to face with white glue, measure out and draw the shape on the plastic, then cut/file the two frame members simultaneously. Ensures both frame rails are identical, and often a lot easier then trying to bend two pieces of rectangular stock to the exact same shape.