The one that inspired me, had me cut out all the double pages, fold them into 'signatures' and hand-stitch them together. Then the cloth inner cover was glued on, and the whole thing dipped into diluted brown paint and shaped into an open book....and left to dry. Then the cover was made and glued on. The video is for a 1/12th scale open book, but I made mine bigger, with more stitching. But the basic techniques are still the same....
*Link to YouTube video with instructions