I run a small building company and therefore have to do a variety of roofing jobs - from small repairs to building extension roofs. I am used to buying building books that purport to be professional guides but turn out to be DIY manuals, American guides inapplicable to the UK, reprints of books that are 50 years out of date or just academic architects guides that don't have practical information on techniques.
This book is spot on.
It gives a good overview of current roofing materials and methods, and then it details lots of commonly faced roofing tasks. The explanations are clear and detailed but if you don't immediately understand there are loads of diagrams and photographs.
While not a complete manual on roofing it is probably comprehensive for anybody who is a general builder, and it is clear enough to be used by a reasonably competent DIYer.
Any criticism? Although the book is 158 pages long I would happily pay for another 300 pages of cleaver solutions to unusual roofing problems.