This is an encyclopedic, large-format book containing hundreds of illustrations. While not geared toward making conventional instruments, Musical Instrument Design provides all the information that anyone (amateur or professional) should ever need to construct an amazingly wide variety of percussion, string, and wind instruments. Includes many designs along with parts lists and detailed construction instructions.
As someone who does a great deal of work in instrument-building (both for my classes and for my own personal enjoyment), I refer to this book constantly. It's a gold mine of information, presented in a clear and straightforward way...with occasional bits of humor tucked in here and there.
An absolutely awesome book if you want to do some experiments with making musical instruments. It covers the very basic physics you will need to make it work and not more. Note that this book is about experimenting, not making professional quality instruments. Also, you should have a work space and basic tools.