I have varied interests. But of all the books I've written, the most enjoyable ones have been those on building acoustic guitars from kits.
Building a kit guitar is like using a modern writing program like Word™ to put together a nice looking document, versus the old, defunct way of having hot type created galleys printed, cutting and pasting a layout, etc. It's easier, but that doesn't make it any less capable of high quality.
With a kit, many years of experience and many hundreds or thousands of dollars of machinery are eliminated. What you get in a box is all the separate parts a professional luthier creates himself, ready to work and fit and make into a really nice guitar.
So, these are the books I've enjoyed doing more than others.