I need a part modeled in 3D to specific shape and size.

I have a lantern project I'm beginning. I need an stl file of a frame that is built to specific shape and size, to match existing piece I have purchased online. Then I need to have an additional cap piece implemented on top section of lantern, (shown in blue tape) so it's closed off to the elements. And instead of the wire frame being only 1/8 thick, it. Needs to be 5/16 each way at a slight angle so I have a place to adhered exterior lantern fabrics. (As shown with cardboard pieces in the photo.) If we can figure out how to accomplish this request, I have other different sizes and shapes I would like to implement.
Thank you
Chase