If I had the necessary skills and tools to make one I would do it. I think the satisfaction from having a home made one is that much greater. Alas, I do love my Zero Image 45. It has all the things that I would probably be too lazy to make on my own like the interchangeable pinhole sizes and zone plates and I can adjust focal length. That alone was worth it in itself as I don't shoot a lot of very wide shots. Flexibility was what sold me on Zero Image, and that was also its appeal over the mighty Harman's Titan. Although Titan 8x10 system sounds very appealing.
Have fun building and show us your progress!