I would be concerned that because the gazebo probably has a raised floor that keeping the heat in during the cold months might be difficult and expensive. I am sure the covering rigid vs poly would be easy enough to figure out with your sons help but before you start think about the heating issues. The greenhouse forum on gardenweb might be a good place to post, lots of experience there.

Hopefully someone can chime in with some first hand knoledge.

Mike

I have owned two houses where I have had greenhouses built off the back but neither was a conversion. The last one was the most efficient. It had a foundation with a knee wall but no solid floor and I had ferns and begonias growing under the benches. There were cedar steps and planking in the middle that we used to access the plants. One thing that I regret not doing was adding a ceiling vent. There were two side windows and a door but still, way too much heat would build up in it, even though we used shade cloth during the summer months. Hope this helps.

lisa