Finally, a comm for that one user who hand-makes longbows. This ones for you, comrade.
If you can access a lightburn machine or alike in a library or a hacklab, I'd cut a set of shelves/boxes from plywood. There are model files around on the internet that can be fairly easily customized to whatever dimensions you need.
We have organized half our life with such setups, I have a plywood shelf like this for spices too.
I use some of these for my indoor plants too and just put a glossy varnish on them, easy to clean and is resistant enough to moisture.
They have a makerspace at a local library!
It's open two days a week within normal working hours.
God forbid someone other than students or retirees used those facilities.
Oh that sucks.
We do all our craft stuff in our local hacklab. I am assuming you are somewhere from Scandinavia so there might be one such makerspace somewhere near you.
If you didn't already solve this, may I suggest the material "corrugated plastic" which is the stuff they make lawn signs out of. Has the benefits of cardboard but is plastic therefor cleanable.
If you make a base out of wood or plywood, you can make walls and sections of corrugated plastic. I've also used combinations of wood, plywood, cardboard, foamboard, hardboard, plexiglass, metal, plastic canvas and random scrap plastic to create the perfect box for a job.
That said I can't follow at all what you are actually hoping to build.
Did the Baron Harkonnen write this title?
You need like a box and dividers, which can be literally sheets of plastic with halfway cuts where you criss-cross them (like 2 combs at a right angle), preferably with lower walls than the box. You can either make them fit snuggly so they wont rattle, glue them in or just don't bother and enjoy rattling
You'll need like a sheet of plastic, a saw, or a hot knife and ventilation, and a box
Any projects you do with wood, you can cover with (foodsafe) varnish to make them easy to clean. This will be a very fun way to learn basic woodworking! Whatever way you design things, assume it will take you at least 10 minutes per cut and 10-15 minutes of assembly per join to accommodate mistakes and triple-quadruple measuring. This also allows for the hour of "everything looks right but this last piece won't slide into place...." jiggerypokery.
Whatever design you make, get 20-25% more material than it requires because you are going to fuck up but it will be okay and help you learn.
Also balsawood with dividers will probably be strong enough for your purposes, is readily available, easily joined with wood glue, and can be cut with an exacto knife.