30 is much easier! Some gardeners like to incorporate misting systems as well as thermal heat syncs which require easy access to water. What are your power requirements? Can your electrical panel handle the extra load of the greenhouse? If you wish to heat your greenhouse with an electric heater, you may need to incorporate a sub panel with 220 volt. Depending on your climate, a 4KW heater would require more voltage than a typical 115 volt outlet, and with the addition of fan system, most large greenhouse gardeners will need additional power to the greenhouse. Is your yard level? How do you access your site? Sloped yards require more planning and may take more time to build. Your yard access may be an impor- tant point should you require any specialty equipment.