THE real answere is what hardware u r using.if u r using 2x 9775 8 core and u r playing 10 min game a book of 10 depth is enf .which any commercial book will do .if u r using a week hardware and play a blitz game and do not bothere to make ur own book use a book created by henery up to depth of 100 moves.this book is called compmaser 1.0