I don't have a cat, or probably never have it, because of a killer allergy, but that doesn't stop me from wanting it often, and even more so when I see things like this giant milk carton for the cute kitty to sleep. Although good, the same for a tiny dog is also valid.
Is about a MOISSUE design, a cardboard house for our pets, shaped like a milk brik - not ours, but the usual one in the United States, for example - only that is significantly larger to fit a medium sized cat or a tiny dog.
I like several things about design: simplicity, originality and decorative versatility. It attracts attention without being strident, and in addition, we can decorate the box as we want, either with adhesives or even with a marker pen if we have some skill.
It is not yet for sale, but if it makes you very excited to have one, I would get a good piece of cardboard and a brik with the desired shape, I would disassemble it and try to imitate its design, because it doesn't seem like something really complicated. If the crafts are not your thing, you can wait for it to appear in the designers' online store or ask them for their commercialization.