Available space and cost usually have a large impact on the choice of size for a hobby greenhouse. Keep in mind, however, that a greenhouse that is too small may cost more to operate; this may offset the initial cost of building a larger one.
As a starting point, 100 square feet would be a minimum size, but 200 square feet is better. A house 9 to 14 feet wide by 20 feet long can be managed in a few hours per week. A larger greenhouse can also cost less to cover per square foot than a small greenhouse, so choose a size slightly larger than you think you need.
