your wish is my command:
You could use medium frames - and still have a one sized/roofed box- if you had a ‘spacer’ sitting underneath the medium frames. Or - thinking about it- you could go with a design like your one above- but instead of having the flow end sticking up higher than the rest- have it hanging down below- and flush at the top? That way when you cut the rebates for the frame rest you would just make a single cut all the way along.
In about one week- I should be ready to post photos of my complete hive here.