People have a story to tell and its personal. When helping somebody tell their story it is very much a collaboration of ideas between them and the designer. The designer can present ideas and advise on what is and isn't possible. 

A book layout and design has to represent or echo the content. As well as layout, there are many technical decisions to be made: book shape and size (large for coffee table display or compact for easy reading);  cover thickness (hard or soft cover); inside paper type (photos require thicker, coated paper stocks for best display);  costs (a set budget will determine the above criteria).