There are many many ways to build a cat house.
We can get fancy and complicated and build a DIY cat house with wood.
See for example this GORGEOUS indoor modern cat house inspired by the Eames chair someone made on Reddit:
Or we can go super simple and build a small cat house with a cardboard box and an old T-shirt
Like we did for our rescue kitty when we adopted her!
(She was an outdoor street cat so we needed an outdoor cat house we could leave in the porch for her)
Now the problem with cardboard cat houses is that they are, well not aesthetic cat houses, and they don't really fit our home.
So we came up with the idea of creating a cat house for our cat that fits into the IKEA Kallax shelves, and which fits with our aesthetic.
And you can have it too if you shop here !