So I looked at the pictures of Shiva, my cat, but the one that helped me with the shapes is too dark to show (taken in the middle of the night, would look terrible if I tried to play with the exposure). So you have to believe me that I took that pic and I'm just posting a random pic of her.
And this is the rough sketch:
I added some piercings to the sketch to make her look more punk, as she normally has this "what did I ever do to you human" look (later I decided I'm not gonna draw the piercings). Apart from the look, she's actually the most darling cat. She sleeps cuddling my head.