Greenhouses, Sheds and Sun Rooms - Greenhouse/solar heating

I have a garage with one wall that faces south (in Chicago). I would like to build a greenhouse/cold frame on that wall, as it gets sun all day, all year. I think I can build a lean-to frame pretty easily that will be about 12 feet wide, 8 feet high, and 3 or 4 feet deep.

I would like to put a passive solar heating system on top of the garage to heat the greenhouse in the winter. Does anyone have any ideas how I can do that and where I should start?

I always go to the library first off to research ideas. I came across some solar heating while reading up on green houses. Try the library first and then while you're there ask the librarian if she might know where you can find some U.S. government (dept of energy, agriculture )reports or brochures. I can't remember the titles of some of the books I went through, but I do remember that some were of passive solar houses, and they went through the placement,
angles, and had charts of average daylight sun, etc,etc.
Also there were a few books that had a listing of companies, distrubitors, and outlets or stores that sell the parts.