This page provides information on constructing a pinhole camera, using mine as an example.
 

This is the top view of my camera.  I used a thick
cardboard shoebox, painted it black inside, and covered it in duct tape to make it water resistant (since I was setting it in the snow all month).  It is imperative that the box be light-tight. The material that the camera is made out of must be thick enough not to let any light in, and the corners and edges must also be sealed to prevent light leaks.

You can see the two top diagonal focuing lines on my camera.  The line they both hit is where the film was.  I intended to construct other film holders, farther back, to have a zoom option, so to speak.
 
 
 
 
 
 

This is the front of my camera.  My shutter setup, as you can see, was complicated, but effective in holding light out until I had the camera set.  The pinhole is in that square in the middle.  It was drilled through a piece of aluminum, which I taped to the box.  It is possible to have the pinhole removeable, so that different ones may be inserted, such as a multiple hole piece, or a slit instead of a hole.

Ideally the shutter should be simple enough to be able to open and close without disturbing the camera too much.  Mine had a flap that went down and one that went up over it, and both were taped shut.
 
 
 
 
 
 
 

This is the inside view of my camera.  It must be solid black to prevent light reflecting inside.  The pinhole is to the left and the film is held on the piece of cardboard in the middle.  The carboard is removeable to assist in loading the film (which must, of course, be done in total darkness).
 
 
 
 
 
 
 
 
 
 
 
 
 

In the upper left, you can see the previously mentioned carboard piece.  There is a piece of film held on it for example.  I used photo corners that you would use in an older album to hold my film, and the loading process was easier than I expected.

In the bottom right is my focusing square.  The hole is the same size as a negative and when held the same distance from the eye that the film is from the pinhole, it provides a good approximation of what the picture will be.

In the upper right is a negative envelope.  These protect developed negatives.