Thanks everyone for the replies. Building it around a film holder would be an easy option. And actually, 7x10 is a nice negative size - hahah. However, I still find myself yearning for a larger negative. Now I'm thinking though that even a full 8x10 sheet isn't going to satisfy that need. I might just end up building a camera around a 11x14 negative or a 10x14 would be an awesome size to accentuate the horizontal format. I've thought about just switching to 4x5 film for pinholes but then you lose the long exposure fun of it, developing by inspection, and the challenge of paper negatives.