I thought that it can't be that hard to make one myself! It turned out to be relatively easy to make, at the same time a lot of fun and also I got to choose what cover I wanted. Cheap, personal, cool and you don't even need a sewing machine!
Step 1: The book
I used: 10 x 13 inches for my case (MacBook 13-inch screen)
The thickness of the book does not really matter since I took the cover apart and put 2 zippers all the way around. You can choose a book with a thicker spine if you want to keep it.