Summarize the following:
Whether you build the greenhouse from scratch or build it with a kit, you should choose the size carefully.  The larger the greenhouse, the more money it will cost to build and heat. The most popular greenhouse size is 8 by 6 feet (2.4 by 1.8 m). You can get a pop-up or polycarbonate greenhouse from home improvement stores and Amazon for as little as $150. Larger, sturdier models range from $500 to $5,000 depending upon size. Look at websites like Costco.com, Home Depot, or Greenhouses.com. If you have chosen an area against a building, you may as well construct a simple lean-structure that uses the remaining wall as support.  If you have a brick structure, the heat from the building can help you keep a steady, warm temperature. This is a fairly easy structure to make yourself. You can support it with rebar, wooden beams and fewer supports that an offset building. This is a domed ceiling that can be made with steel supports or PVC tubing (PVC does contains several carcinogenic estrogen mimickers that are water soluble, ldpe tubing is more expensive but a saver alternative.).  The domed shape means there is less head and storage space that rectangular models. This shape can be built with little cost; however, the less expensive the material, the less sturdy it is likely to be. With this design, you will need a foundation and a frame. Unless you are a designer, you will want to buy a plan for a greenhouse or employ someone to build it.  A rigid frame, post and rafter or A-frame greenhouse will need a foundation and a sturdy frame. You will need the help of friends or employees to help you build a large framed greenhouse.

Summary:
Measure your location. Choose a greenhouse kit, if you have little experience building or few people to help you erect the greenhouse. Make a lean-to. Build a Quonset frame. Pick a rigid frame.