How to build your own underwater housing unit for your camera?

I have a Nikon D3000 and don't want to spend a lot of money on an underwater housing unit but would like to take some under water shots. I was thinking going out in the surf and taking pictures of my friends surfing and boogie boarding. It does not need to be able to go to deep just enough for me to dive under waves if necessary maybe 20 feet. Any suggestions on how to build one. Links, videos, anything.

There's ways but I would not trust them with a dslr

20 feet? You need a good housing for that deep, in the case you can find any surfer down there, pressure is nearly double than up here; cheaper glove bags are also available but not for so deep