<--Brian Hankins
Brian,
i don't know of any available plans, because basically all you are doing is 
making a box or a variant of a box. it's the pinhole size i presume that you 
require information on.  
I have built several 4x5, 5x7 and 10x8 pinhole cameras (and a 16x20 - foolish 
mistake that one) to take double dark slides to do just what you wish to do ie. 
take lots of pictures at once to develop later.
Your best sources are: 
1.the Pinhole Journal, which has a whole issue devoted to how to build a 
pinhole giving specifications for pinhole sizes etc which is a wonderful 
shortcut to the trial and error method for finding the diameter of the hole in 
order to produce the sharpest image - if sharpness is a critical factor that 
is! i can't put my hands on the right issue just now. I'll let you know. the 
first couple of issues discuss pinhole size and sharpness. the Journal is a 
great resource.
2. Eric Renner's *Pinhole photography. Rediscovering a historic technique.* 
Focal press (1995) has a great how-to section. this book is largely a 
compilation from the pinhole journal - a *best of* if you like - 
 
Basically, with one exception, I have always simply built a box.
I have made all my cameras out of marine ply or ply wood, put a hinged back 
door with compressable dense rubber around the edges of it to exert a little 
pressure on the film holder edges to keep it firm on the frame. The door hooks 
shut firmly. 
I actually went to woodwork school for 6 months one time because i wanted to 
make a camera (a *twin lensless* camera) and had no skills beyond chopping, 
sawing and banging nails into things. the resulting camera looks good - the 
teacher was very helpful! the rest of the woodwork students turned up their 
noses, sneered and asked me why I didn't want a camera out of plastic and 
metal. they were making tables and hat stands and other useless things. (Well 
you can buy those things in a shop, but you can't buy a camera whcih takes 
pictures from the front and the back at the same time...)
Anyway, decide on whether you want wide-angle, normal or telephoto and how 
rigid or longlasting you want it to be and design it yourself. with that size 
of negative, the camera it is going to be big and bulky and possibly heavy. 
perhaps make it out of cedar or something really light. or even make it 
collapsible with bellows.
Catherine Rogers