4 Sheets of plywood
4 old rags or remnants
That's all it took in materials and there were only 5 cuts with a jigsaw and 4 cuts with a Skil-saw.
I've discovered that my nearby Sutherlands Lumber store sells defect plywood and OSB for 5 dollars a sheet, which is a huge savings. I've gotten 1/4" to 3/4". This project used 3 sheets of 1/4" OSB and 1 sheet of 1/4" plywood for the top, since it gets the brunt of the rain.
Cut 1 - Cut a door in a whole sheet of OSB with a jigsaw. Mine is 2'x2'.
Cut 2 & 3 - Rip 6" off the long side and 1' off the narrow end of another sheet of OSB.
Cut 4 - Cut a diagonal across this piece. I made the long side 4' and the short side 3'. This will leave an identical piece for the other side.
Cut 5 - Rip 1' off the long side of another sheet of OSB to make the back.
Cut 6, 7, 8 & 9 - Notch out spots for the t-posts in the roof of plywood, with a jigsaw.
Make the measured cuts in prep for assembly. Notch out the t-posts after assembly of the sides, because there's no way to premeasure where the t-post is going to end up, unless you are much more careful than I am, when you pound in the t-posts. I needed this done fast, so that I would have a little time left over, to post the pictures here..
I assembled the whole thing with nothing but baling wire, to make it even cheaper. The t-posts are the main structural members. The wood is nothing but a weather shield.
Once the top is on, I wrapped the t-posts with old rags before I tied it on with baling wire. This will prevent direct rain from going in, and being on top, the rags will dry out faster and be less likely to rot the wood over time.
You could also use this same method to build a hog house. But, I would use 3/4" plywood all the way around because hogs can really tear stuff up when they get mad at it.