Eco Greenhouses are a modular greenhouse, which gives the gardener the ability to customize the greenhouse to their needs. The front, back, and middle sections of our greenhouses have all been been packaged separately. So for example, if you purchased an 8' x 12' Hobby Gardener, you would receive 1 front, 1 back, and 2 middle sections. If instead you purchased an 8' x 20' Hobby Gardener, you would receive 1 front, 1 back, and 4 middle sections. If you want to expand your greenhouse at a later time you simply add more middle sections. We can also substitute the back section for a front section (one front on each end) to create a walk-through style, dual-door greenhouse.