If you live in a climate zone where the winters are cold, then building a greenhouse will allow you to grow plants that require controlled conditions. The type of greenhouse that you choose to build will depend on the space that you have in your yard, the required growing area, and the budget that you have for the project.
In selecting a location, the most important thing is to assure that the greenhouse will get maximum sunlight. Ideally, this means locating it on the south side of your home. If you have to, you can locate it on the east side of the house because morning sunlight will get the plants producing food early in the day. Carefully measure the dimensions of your location so that you can determine the maximum footprint for your greenhouse. And make sure that the site has drainage and access to electricity, water, and heat.
You have to determine the type of greenhouse you will build. An attached greenhouse becomes an extension of your home and requires just three walls. A free standing greenhouse will be a four wall structure and can take any number of shapes to make best use of the space available. For a free standing greenhouse, you will have to install separate heating, electrical and water systems. The smaller the greenhouse, the greater the ratio of glass area to floor space. Thus you have a proportionately greater area where heat is lost or gained and with a lower inside air volume, temperature changes can occur more quickly.
You can construct with different frames including, Quonset, gothic, rigid frame, post and rafter and A frame. You can cover the frame in traditional glass, fiberglass, double wall plastic, or film plastic. Glass gives the best light penetration but is vulnerable to breaking due to hail or tree limbs. Fiberglass is break resistant and should last up to 20 years. It will require more maintenance than glass. Double wall plastic will retain heat better, thereby creating energy savings. But it will reduce the amount of light coming into the greenhouse. Film plastic is very light and allows excellent light. But it will need to be replaced every 18 months.
You will have to dig a foundation, but there is no need for permanent flooring. Install a three foot wide stone walkway to the plant areas and then lay gravel over the rest of the floor to insure proper drainage.