I modeled up this simple pinhole camera so I could have a re-usable setup that can be easily adjusted. There is are two slots running down the back wall that are sized to hold standard 5" x 7" photographic paper. I placed a large rectangular cut out in the front face. The intention is to tape a piece of card stock or aluminum foil over the hole and then poke your desired pinhole in. 

I printed mine in black PLA, but I think plenty of other filaments should work just fine as long as they are dark enough to keep out light. I would also suggest upping your perimeter count to assist with this.