As an absolute minimum, you could make this with a claw hammer, a saw and some nails. I've been lazy and used screws, but I've also been reclaiming nails from pallets, and I think you could get enough together.
![Image](https://i.postimg.cc/2yyrfBpV/1.jpg)
The box - I've reduced the size of it to fit the piece of polycarbonate; no better reason. It would be neater to keep it the right size, but such is life! Cut two long pieces of pallet wood; you'll need them as a sort of bench.
![Image](https://i.postimg.cc/m2cBXMNn/2.jpg)
Cut two corner pieces to help provide rigidity. I've had to cut down the front piece as I couldn't get the corner bits off without removing the rivets. You could definitely do a better job.
![Image](https://i.postimg.cc/LX6MzZ8N/3.jpg)
Screw the pallet length above to give it rigidity before sorting the front piece out.
![Image](https://i.postimg.cc/WbQjQ351/4.jpg)
![Image](https://i.postimg.cc/vTKM8HMX/5.jpg)
![Image](https://i.postimg.cc/g28ddW7q/6.jpg)
Two lengths now, to put the diagonal section in. You'll be able to see the form coming together.
![Image](https://i.postimg.cc/6QhX2ht8/7.jpg)
I've trimmed them in situ; it seems easier.
![Image](https://i.postimg.cc/hGnntYWF/8.jpg)
These are old radiator brackets, but will be handy as feet to peg the thing down.
![Image](https://i.postimg.cc/PfVdQKZZ/9.jpg)
Right, the box is now assembled with rigidity.
![Image](https://i.postimg.cc/85KgwPFD/10.jpg)
We three lengths of pallet wood!
![Image](https://i.postimg.cc/h4YqdvW1/11.jpg)
Put the three together, and make some shorter ones (length can be hit and miss) to make up the back panel.
![Image](https://i.postimg.cc/fyVnPnXd/12.jpg)
![Image](https://i.postimg.cc/hP7RbnKW/13.jpg)
![Image](https://i.postimg.cc/YCKKdPS4/14.jpg)
The diagonal can now be added.
![Image](https://i.postimg.cc/jSHVmhWM/15.jpg)
![Image](https://i.postimg.cc/MHg22PbF/16.jpg)
I find it easier to trim them when they're in situ.
![Image](https://i.postimg.cc/MG5CKKmR/17.jpg)
So, you can do this two ways, either with a protractor, or with a pencil and a straight edge, which is the way I did it. You could do a better job for sure with a mitresaw...
![Image](https://i.postimg.cc/ZqJkSyp4/18.jpg)
![Image](https://i.postimg.cc/ZRq19twQ/19.jpg)
A piece behind, screwed from the inside, will help you to place it all.
![Image](https://i.postimg.cc/vBSCfqjZ/20.jpg)
![Image](https://i.postimg.cc/wMyZV58c/21.jpg)
![Image](https://i.postimg.cc/Kc18VdmQ/22.jpg)
![Image](https://i.postimg.cc/Y2TCwb97/23.jpg)
![Image](https://i.postimg.cc/C53t6Zwy/24.jpg)
![Image](https://i.postimg.cc/P5jfCJYF/25.jpg)
![Image](https://i.postimg.cc/8PWPkMJ6/26.jpg)
![Image](https://i.postimg.cc/TPkTNcSZ/27.jpg)
![Image](https://i.postimg.cc/kXxqPCzN/28.jpg)
![Image](https://i.postimg.cc/ZqYTLQf8/29.jpg)
![Image](https://i.postimg.cc/V6pmmkzg/30.jpg)
![Image](https://i.postimg.cc/wv7gCmY3/31.jpg)
![Image](https://i.postimg.cc/HnMHx1xg/32.jpg)
![Image](https://i.postimg.cc/KvXxWjqv/33.jpg)
![Image](https://i.postimg.cc/YCR7j3ph/34.jpg)
![Image](https://i.postimg.cc/dVwvqXcb/35.jpg)
![Image](https://i.postimg.cc/25Xf7SLY/36.jpg)
![Image](https://i.postimg.cc/tggj6xTD/37.jpg)
![Image](https://i.postimg.cc/85JgKgL6/38.jpg)
![Image](https://i.postimg.cc/j5p0B3hk/39.jpg)
![Image](https://i.postimg.cc/7PzySDHv/40.jpg)
![Image](https://i.postimg.cc/Xq9SWKHN/41.jpg)
![Image](https://i.postimg.cc/Gh1nQNt4/42.jpg)
Taaa-daaa! Just some painting to sort now :)
I'll add more notes as I go, if I can. I'm going to paint the outside to slow the rot, but otherwise not looking at a huge amount to develop.