Hanna in Sweden has a good tutorial for sewing a hooded pet bed—perfect for a cat or small dog. This project will be easier with some sewing experience, but is still pretty straightforward. She gives details for how to size your pattern, but you’ll have to make your own. Don’t let that scare you though. The tutorial combines machine and hand sewing. I would machine sew as much as I could and hide the seams in the folds on the inner part of the bed where the sides attach to the bottom and to the hood.
Hanna used an old curtain, which is a great and very thrifty idea. Material used for drapes is heavier and more durable. You’ll also need foam rubber. She used thinner foam—one layer for the sides and multiple layers for a cushy bottom. You could do that, but buying a thin piece for the sides and a thick piece for the bottom means less cutting and that the foam in the bottom will be easier to manage.