Passive solar roof materials

I live in NW Arkansas and in the process of building a passive Solar Green house.  My south facing roof is 30' X 15' at 45 degree angle.  My question is what glazing would be the best for that roof?  Has anyone in this area built a green house this size and how does it work?

Hi Douglas, I used 6 mil greenhouse plastic on mine (20' by 40').  I wanted two layers of poly so I put a spacer on the trusses between the layers.  That doesn't work all that great so I'd do an inflation blower next go around.  The poly starts out taut but gets saggy when the sun hits it and the layers touch.  The plastic doesn't last that long (4-8 years) but it's cheap.