This site has an incredibly cool step-by-step on how to build your own pinhole camera.

The camera can be built using normal appliances and stuff that you have in your house normally. Some of the pictures shown taken by this camera is quite incredible.

The aperture of the camera is about f/90 and I am not sure what the focal length is but I believe it is not too far from a 50 mm lens actually. This means that exposure times in broad daylight is 2-3 seconds, in cloudy conditions 5-8 seconds indoor is 5-10 minutes or so but it is cool to have built your own camera.

Here are some pictures taken with a pinhole camera by the original maker of it. Alspix profile on Flickr here.