I recently read "Bike, Scooter, and Chopper Projects for the Evil Genius" by Brad Graham and Kathy McGowan, not sure how much ebike-related content it would have. I was pleasantly surprised at the writing style, but it didn't have a lot of ebike info in it.
What it does have, though, is great in-depth instructions on how to build your own, well, as the title describes, bikes, scooters, and choppers, as well as trikes. Several of the projects detail the installation of electric components as part of their design, but they're not all pedal-based, and thus not street legal.
One thing I did really like about the book, though, was that the author gave thorough instructions and pictures about building some pretty fundamental pieces. You may never want to convert a car rim to a spoked bicycle wheel, but if you do, he's got the play-by-play.