http://www.youtube.com/watch?v=kUYok77mMCkThis guy built one of a hypoxic/hypobaric chamber and I want one too. He also won the Tour de France but they said he cheated b/c he used this, and he may or may not have used other things, but who knows.
Looks pretty simple, but I couldn't find any blueprints for it. Darren Sharper of the Minnesota Vikings uses one daily too.