Plans? You don't know me very well, do you ...
I'm a cobbler! A retired teaching living on $1200/month!
The open wall space (no cabinet blockage) inside the kitchen on that south wall is about 8x7 - so the box outside is 8x7. You need intake vents that equal about 50% of the box width. Same for output vents.
Built a simple box frame (8x7) of 2x4's. Screwed 1x6 sides, and 1x8 top and bottom, onto the 2x4's. Caulked between clapboards and frame.
Run black aluminum screening from the bottom (attached to the clapboards) to the top (attached to the top outer edge of the frame). That way the rising air has to pass through the heated screening to reach the top vents.
Tack 1x2's across the outside of the box, one vertical, one horizontal. These support the clear plastic sheeting.
Finish by tacking 3.5 mil clear plastic sheeting across the box; reinforce the edges by tacking 3/4" molding onto the 1x edges.
Voila!
If you have to buy all new materials, might be over $50. Heaven forbid! So I scrounge what I need from the garage, cellar, workshop, and "town recycling center" (the dump). Only new thing I got was the $6.99 roll of clear plastic sheeting. (10' by 100').
Got the idea from Mother Earth News:
https://www.motherearthnews.com/Renewable-Energy/2006-12-01/Build-a-Simple-Solar-Heater.aspx
Tom
a/k/a Frugal Zealot