Well, I haven't had any need yet to make my own plate holders. I'm getting closer to making my own plate camera to fit some of the holders I have, though - among them several stereo plate holders that might make a nice little panorama camera. With a decent lens for 4x8", which shouldn't be too difficult. I think a 90/8 Super Angulon could do it, or something else I'm sure to have lying about already. Weitwinkel-Aristostigmat or something.
As I always seem to do, I'll recommend Alan Greene's book of 'Primitive Photography.' He shows designs for fairly simple folding and box-in-box cameras as well as (wet) plate holders and simple lenses. The diagrams could be clearer, but as I look at blueprints all day, maybe I'm just a little picky. Excellent book though.