The greenhouse kits featured here are mostly beginner models, but they offer a variety of functionality. Before you choose a greenhouse for your needs, I'd recommend reading Before You Buy a Greenhouse, to determine just what those needs are.
Here's a nice size, sturdy, starter greenhouse for areas that don't get too cold in winter or for starting plants in cold climates. The frame is galvanized steel and it's strong & stable enough to hang plants from. The siding is 3-layer polyethylene film, with UV protected roof and doors.
Ventilation is provided by zippered screened side vents. No foundation is required. Assembles with an adjustable, not included. Price Range: $400.00.
We're still talking about greenhouses for milder climates here, but this little conservatory caught my eye because you don't often see plastic greenhouses with so much style. This is a round conservatory, 10' high and 9' in diameter. The frame is galvanized steel and the siding is polyethylene with rip stop protection. Zippered front door and side windows are screened, for venting. Comes with ground stakes, tie-downs and a shade cover. Easy assembly. Has access openings for a water hose and power cord. No foundation is required. Measures 10' H x 9' W x 9' D. 3 year manufacturer's warranty. Price Range: $390.00.
Now we're talking about true greenhouses. The Rion Hobby Greenhouse comes in a range of sizes and a couple of style, but they all have side sheeting that is 6 mil polyethylene with 93% light penetration for up to three years.
The frame is weather resistant heavy gauge extruded aluminum. Assembly is an "easy lock fastening system", which is supposed to provide a perfect seal, for better temperature and humidity control. 2 extraction vents. A true door, rather than a zippered flap, also improves insulation. And it really is tall enough (8') to move in comfortably.
Includes ground stakes. The manufacturer says it assembles in 2-4 hours with a phillips screwdriver and pliers. Price range: $1,800 - 3,000.
Here it is, the greenhouse kit for those of us who aren't especially handy. The frame snaps together without much hardware to fuss with. The side panels, or "SnapGlas" panels, slide and lock into place and the doors and vents come pre-assembled. If only they would come and water my plants, too.
Granted, it will take some time to get the whole thing together, but it will save you some frustration and it's not at all bad looking. The sides are very clear, letting in lots of light, and the ventilation works well. Price range: $800.