Do a search in the Make website for ideas!
Put something that focuses the incoming light in front of a shutter, in front of a light sensitive material. You may use more or less parts as needed (such as an apereture)
I can't help feeling that we would find answering your question a lot easier if you actually asked one! Do you want to make a simple pinhole camera or perhaps use parts from old disposables to make something use for time-lapse studies? Give people at least something to work with & i am sure you will get a response.