f295.org has a whole sub-forum devoted to building pinhole cameras - might want to search/ask there as well.

Also, jnanian (John) has been making some of these LF box cameras lately in various sizes for sale out of foam core - not specifically pinhole, but a pinhole could be fitted in place of the (basic) lens. The foam core ones he's made are not terribly expensive and include some basic film plane movements - might be worth sending him a PM, even if you don't want to have him make you one, he's a nice guy and generally quite helpful and may be willing to share some construction tips