After many years of yearning for a greenhouse I purchased an 8ft X 6ft model from Harbor Freight. The box says it's manufactured by One Step Gardens, but I believe they specifically make products for Harbor Freight. The nightmare started when we cut the box open.
As you would imagaine, there are a gazillion parts to an 8 X 6 greenhouse that comes in a cardboard box. Once we sorted out all of the parts listed on the lame instructions, (and yes, all parts were there, I'll give them that much), my husband and I dove into the assembly of the project. Most of the manual consisted of bad illustrations and poorly translated English. Arrgggh! At one point we were so stumped on how to put one part together, I went to my computer to see if there were better instructions on the internet. Voila! I found the perfect website with REAL pictures. (* see below) It saved our marriage!
Long story short, after one winter of heavy rain and wind, I chased and hunted pieces of my greenhouse all over the neighborhood! The window clips supplied are minimum, so I ordered more through a garden supply. That still didn't keep my polycarbonate windows in place. We ended up applying silicone around the windows and are awaiting the upcoming winter season to see if this helps keep parts from flying in the wind.
When the construction DID hold together it was a nice place to winter-over potted plants and start seedlings in the Spring. You must construct a base and supply heat when colder weather threatens plants. If you're worried about high electric bills in the winter this is something to consider.
The bottom line is, save up and spend a little more on a greenhouse with better quality. If you still want to buy the Harbor Frieght Greenhouse be sure to go to the website below to aid with the construction...and buy silicone.