How can I make bespoke storage boxes?

[ButternJam]

I want 7 bespoke sized storage boxes with lids (preferably cardboard) to exactly fit in my shelving units. I can't find anything commercially available to fit. I can't even find a cardboard box manufacturer who can make them tall enough. Can you think of a way I could make some without too much stress & strain? I need:

34.5cmW x 31.5cmH x 25cmD (x3)
&
37cmW x 31.5cmH x 25cmD (x4)

Any ideas welcome.

I would see what’s the heaviest gauge cardboard you can buy from eg hobbycraft. If that’s not sturdy enough then buy some big moving boxes and cut down (or try and get hold of some free). Make a paper template to experiment with best method (I bet there’s one online) and go from there!

There are some YouTube tutorials - like this

Correx might be a good material. It's like corrugated cardboard but made of plastic. You buy it in big sheets, and you can cut it with a Stanley knife. If you Google c&c cages for guinea pigs, you will come across suggestions of where to buy it.