When hiring a contractor it is helpful to find someone with experience in constructing a greenhouse.
The most common mistakes contractors make are:
Letting a contractor do the design too. This may result in in poor cooling, the use of improper building materials that can’t withstand the humidity and temperature swings, and poor lighting.
If you can’t find a contractor with experience be sure to read everything you can on constructing a greenhouse. The first few chapters of the Greenhouse Gardener’s Companion can be a big help. Also visit at length with experts at greenhouse material companies such as Charley’s and Sundance Supply (see ads to the right).