I was able to find a few websites that kind of told how to turn a disposable camera into one.
Here's what I did.... if I remember correctly (I made mine a few months ago)
Buy a disposable camera, PREFERABLY ONE WITHOUT A FLASH OPTION!
Then, take it apart... there are little tab-like things on the top, bottom, and sides of it, and it'll open into two halves. Then, I removed the shutter so there was no glass/plastic or anything there, and I taped a bit of tin foil with a pin hole in it into the inside where the lens would have been. Just put some thick black tape over the hole on the outside so you don;t let any unwanted light in!
Then, I put in some new film, which was incredibly difficult because i did it at home with no dark room so I had to go in a super dark bathroom and it was creepy! This part was tricky, but I think I just connected it and wound it up. Then I put the camera back together and used it like a normal pinhole, but I still had to manually advance the film by spinning the wheel thing. Oh, and once I put it back together, I taped up any holes or cracks with the thick black tape.
I hope that helps, sorry if it was confusing!
Be sure to post your pictures if you give it a try