Turn that old portable metal pipe carport into a greenhouse.
I used one section (out of 3) of an old metal pipe portable garage (the plastic cover rotted off) for the starting frame.
Using the carport's shape, cut wood to fit the frame. Most of the wood was from 2x6's cut in half long ways (ripped).
Although I used 2x6's across the front and back because it is a 9 foot span, since the window frame would support it, you could use smaller lumber instead. I used a 4x4 I had laying around for the side with the door. The ground here is at an angle and I wanted to be able to step on the door sill without it bending too much. The window frame is from 2x2's.
The 10 foot wide plastic fit perfectly with just a little trimming.
First cut each piece of wood to fit the frame and attach to the metal using pipe clamps held on with flat metal plates screwed into the wood - no need to drill any holes in the pipe.
(hint: you have to screw the clamps to the wood with the metal plates before attaching to the pipe - experiment to get the screw on the pipe clamp in the right place.)
The frame had a tendency to wobble a bit front to back so, for the sides, I attached crossing guy wires to eye bolts on each side using tighteners, and now it is very stable.
The bottom sill on the back sides didn't have room for the pipe clamp tightener so I used metal braces.
I used metal plates on most of the joints because I happened to have them. You could use plywood or some other method just as well.
The whole thing is held down with stakes, cinder blocks on the low corners, and railroad ties around the outside (just in case).
Make a frame for windows using 2x2's.
I got automatic window openers so it wouldn't get too hot inside and boxed in a frame for them from 1 inch wood and lapped the ends, attached a hinge to the top of the window, and covered the window with the plastic.
I used 6 mil clear plastic like they use on crawl spaces under houses. I only used half the roll, so if it doesnt last in the sun I can put the other half up and it's still a lot cheaper than greenhouse film. I stapled it on and then screwed 1/2 thick strips of wood over the staples so they wouldn't pull out in a wind. The door is a simple frame with plywood braces on the corners, hinges, and a gate latch.
The shade cloth on top is attached with snaps to the railroad ties in case it gets really hot. It is easy to pull it out of the way when its not needed. The black painted 55 gallon drums help hold in heat on cold Oregon nights.
The plants loved it.