Finally! I have my own small walk-in greenhouse! After starting seeds indoors and moving them to finicky, bulky mini-hoop houses for years, I can actually walk into a space that's flooded with seedlings in an easier-to control environment. You can do this, too, even if you're not very "handy." I don't consider myself "handy," but I'm willing to learn and try new things, and that seems to work (with one proviso: my method of building this was VERY cheap - total cost was $137 - and because I used PVC, thin 2mil plastic sheeting and not a more expensive, thicker UV-resistant sheeting, and plastic tie-wraps, I know this structure will need regular maintenance, but ultimately I think it will be a better investment than a pre-fab unit, for the reasons outlined here).
So here's how to build your own 6'x10' lean-to greenhouse:
1. Drill a pressure-treated 2x4x10 with 1" holes drilled every 2 feet level into studs along the back wall on the south-facing wall of your home. I lined this up with the halfway point on one of my windows for reasons described below.
2. On the ground 6 feet away, hammer 1/2"x2' rebar 1 foot into the ground spaced 2' apart, lined up square with the holes you drilled on the 10' board on the wall.
3. Measure and attach a 2x4 vertically from your top board to the ground surface, and attach another measured and cut 2x4 along the ground (checking to make sure it's level) using heavy-duty tie-wraps.