I thought about buying this book over Christmas 2020 and spent the first three months of 2021 considering how and more importantly if I would follow its instructions.
On the surface the book appears to be a complete guide to building a decent looking shed-come-garden-room, with pages throughout adorned with beautiful illustrations on how to do things. However this is no idiots guide; while it does show you step by step how to do certain things almost every section of the book is written with some assumption of prior knowledge and I found some sections to have inconsistencies between steps.
With that being said, this book is an excellent rough guide and will get you far enough along to have a base, four walls and a roof framed out; leaving you, the reader, to learn elsewhere how to do the details such as sheathing the walls and house wrap (something the book leaves out entirely).
If you couldn't have guessed by now, I did in fact decide to follow the book; having been ground down by the extensive lock-down due to the ongoing pandemic I spent a couple of weeks building my garden office. The book now battered, soiled and ready to be retired has served me well however I did not go about the endeavour with the book alone. You will find it a most excellent starting position, but YouTube guides and asking people on various forums will get you over the finish line.