75
This depends on many factors. It depends on who is going to build the greenhouse. How big the greenhouse will be. Also where the greenhouse if being built.
28
You will need at least 13-9' 2x4's, on 16" centers, and 2-16' 2x4's for plates. (Deduct plate thickness from stud length)
56
The most economical way to build a greenhouse depends on the location. If the location already gets a lot of sun use it.
Glass mostly. A greenhouse would need sunlight.
is 60 2'x4' to many
OH, and its about 7 feet high
Walls are commonly framed with 2x4 lumber, known as studs. The covering is fastened to the wall to enclose it.
The easiest way is to build a rough frame out of 2x4's. Put two vertical 2x4's at the ends, out from the wall to make the shelf the desired depth. These rest on the floor and need no further support once the shelves are attached. Then build rectangular frames for each shelf you want. fasten these to the wall and the vertical 2x4's at the desired height. use 1/2 or 5/8 ply for the shelf surfaces. When I build these I make the shelve 18x84 inches to get 3 shelves form a sheet of ply.
2x4-56 2x4=8 8-56= -48)