When you buy a book on Google Books, it will be stored in your ebookstore. Go to your ebookstore and click on the book you want to print. There will be a button that says "read now" and right below that, you want to click on "read on your device." At the bottom, there is an option to download as a PDF. Just download it and print it from there. There will be a Google watermark, but at least it's a hard copy!