I just built a glass greenhouse two years ago but I used twinwall polycarbonate glazing for the roof. The twinwall is less prone to breakage and disperses the light a bit as it passes through it.
I still use shade cloth in the summer as the sun is directly overhead and would be unbearable otherwise inside.
Another suggestion...get TREMCO 830 sealant, it's pricey but you will not regret it or ever have to re-do it.
Keep us updated, I'm interested to see your progress.
