Hmm (since this popped up again) -- in my earlier answer I interpreted the question as being about the actual pinhole plates rather than the entire camera. Stepping up the hierarchy to the entire camera, I've been a little less DIY -- sort of. A pinhole lens board for a 4x5 press camera was my first effort, a pinhole body cap for my Bronica SQ-A was the second. The third effort, in 2011, was a complete from scratch 4x5 (= UK 5x4 ) except for using standard filmholders.
Almost everything I've ever done with pinholes is online for what it may be worth. I must confess to a few impure thoughts about something larger, but it probably won't happen this year.