I've had my Arcadia Glasshouse greenhouse for 8 years now and it's been great. It's partly under a black walnut tree so I get walnuts dropping on the roof every fall. It makes a horrendously loud noise but no damage at all to the polycarbonate roof (hope I haven't jinxed myself). It's very well built.
Customer service is outstanding too.
Go as big as you can afford. Dealing with the city's permit process is nothing compared to wishing you had more space. It's very easy to fill up a greenhouse, plants grow, your culture interests expand . . . My GH is a lean-to, easily accessible from the house. It's paradise to walk out there in the winter.
