I traced the door onto a piece of foam core so I can cut out a piece from which to make the red and black door frame. I test-fitted the door, and it seemed to be okay.
Then I proceeded to glue a layer of paper onto the inner foam edge to provide a surface onto which I can glue and paint the final pieces. After trimming off the outside edge of the door frame, that received a layer of paper as well.
I glued the door to a thin later of styrene which will provide the back side of the door. I gave the plastic door a couple layers of paint... not much to explain about that!
When the paint and glue were dry, I once again test-fitted the parts. Now I can proceed to making raised pieces for the door frame and prepare the surfaces for painting!