I made this one - I never wrote down the instructions for it but can probably recall the list of materials. I donated it to a Humane Society so I have no way right now to do exact measurements but can come close enough. How detailed do you need it to be? Is the person who is making it handy?
It's in line with the wooden ones. Ain't pretty, but it doesn't need to be pretty to catch those hard to catch ferals.
I didn't read all of the instructions, but we discovered this by accident: If you place the trap on a concrete surface, it can shift if the cat pushes hard against it. To prevent that from happening, get a strip of rubber and put it under the side of the trap that stays on the ground when it is set. The alternative is to glue rubber strips to the bottom wood boards.