I used to know of some rack plans for adult ball pythons but it's been a long time since I have seen or referred to them. Sorry. They are out there, I just don't have them. Racks are very straightforward so you just need some basic ideas and then modify the plans for the box you decide to use.
A former frequent poster on this forum posted a tutorial on building racks for large boxes. I think his user name was Rainbows-R-Us or a similar name. Maybe track him down on the Rainbow Boa forum. He's a great guy.
Regarding Home Depot, I have had good and back luck with having them cut sheet goods on their panel saw. I don't blame you for wanting to avoid that.
However, many years ago I had very good luck with a local cabinet shop who both sold me the melamine and cut it to size for me. Very reasonable prices and the melamine was very nice. From my experience just about every cabinet shop is happy to have something to keep their entry level floor guys busy and to keep their machines running.
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Currently keeping a small collection of various Gonyosoma. Both G. janseni and G. oxycephala.