My local library has a book with the instructions on how to do it - ironically enough I am making one tonight - The book it is in is called Singer Quick and Easy Sewing Projects. It is relatively easy - especially since I am a novice sewer and have had pretty much no problems making it - but there are a lot of measurements for different sized finished sizes . I wasn't able to find the directions online anywhere sadly.
Maybe your local library might have this book? It is a very common book.