PVC Reducer. Navigating the PVC section of the hardware store might be a bit tricky. What you're looking for is the piece that functions to reduce the pipes from a larger circumference to a smaller circumference. The smaller circumference will be what fits around the lens barrel of your camera, while the larger circumference will comprise the “hood.”
Bring your camera with you, so that you can try fitting various reducers onto your camera to see what will fit, and what won't obstruct the periphery of your shot. Now, be aware that for some point and shoots the lens barrel will not extend far enough out to really have an effective rain hood.
Black is the best colour for the PVC, as it will cause the least corruption to any light that bounces off the inside of the reducer and into your sensor. Failing that, a little sharpie or paint can do the trick.
Sandpaper. Many reducers have bevels, which may need to be sanded down to make that fit absolutely perfect. (Note that these bevels might prevent you from fitting the reducers properly at the hardware store.) You might also need to shorten either side of the reducer so that you don't get that vignetting effect from an overprotective lens hood! If it looks like you need to do some serious material removal, it might be a good idea to get a file.