I've been thinking about this for a while now: a 10x8 format camera to take paper negatives and (with added prism) direct positives with mirror-image correction. It was the latter requirement that made me decide on a pyramid-shaped cone. Then, worrying about weight, I decided I'd make it out of papier mache.
The paper is actually the first draft of my first novel (shameless plug: "The Building" by John Nelson available for Kindle download at...http://www.amazon.co.uk/The-Building.../dp/B00QMMXKP2)
The cone will be attached by hinge to the darkslide tray which will have a wide tripod base plate. I'll be using a 0.5mm pinhole and (when needed) a right-angle prism. I'll post progress as it occurs. Cheers.