A clear plastic roof may be just what you need. You can get clear corrugated roofing at your local building supply store or try something a little different. The material in this photo is 1/2 inch thick honey comb plastic from Tap Plastic. I think it looks a little more upscale and diffuses the light nicely.
Conservatory styles. Thinking the P shaped would be good, could have living space in part and greenhouse in part, or maybe two Edwardian, one connected to the house, one separate but easy to get to, for greenhouse.