You didn't mention your intended use, or details on your climate for the intended use seasons. That's important for overhead glazing, especially for summer. Around 20% glazing on roof is plenty for summers and gets you by in spring/fall here in central eastern AZ at 5600ft. Those with more just end up covering it with shade cloth, unless massive evap cooling is used (that's what the big pot farm does). Excess overhead glazing costs you in winter, thermally, and adds little to insolation in winter.
Greenhouses with triple or quad pane polycarb roof (which reduces sun somewhat) and no forced air evap cooling don't get used here in the summer, it's just too hot, even with massive patio doors open. Outside highs of high 90's and low 100's. Ventilation is a bad joke when the outside air is 100F. Our humidity is dry so evap cooling is possible, with 20F temperature drop over ambient. If it's humid where you are, summer use of the greenhouse may be impractical.
Intended use and in what seasons is also HUGE in design impact; if it's early spring starts only, that makes things much easier.
