Nothing could be simpler than a light-tight box with a lens (of adequate
coverage) at a fixed focal point, with a location on the rear for film.
Unlike most large format cameras, there is no bellows (which would allow
focus plane manipulation and focus itself).
The simplest implementation would be something like a cardboard box with
a piece of film taped on the inside rear surface and a lens somehow mounted
on the front (fixed focus).
The more elegant solution I have seen (Jay Dusard) is a nicely crafted
box with a ground glass on the back and a 90mm lens mounted on the front
in a helical focusing mount (screws in and out to move the lens location
with respect to the film). Nicely finished.
Probably the most difficult engineering you'd do to duplicate Jay's
experience would be the rear ground glass assembly --- it must place
the g.g. focus point at the same distance from the lens as the film
holder does, and the film/gg focus must be perpendicular to the axis
of the lens (unless, of course, you design keystoning in your images :-)
Film holders created from cutdown Fidelity holder material are available
from Canham. (And Wisner has some other style that some may prefer).
Have fun!