Some of the coolest reptile enclosures are made from things you would never think of. I couldn't find the thread, but I remember seeing a guy make an enclosure out of an old hollowed out console TV. A little ingenuity can go a long way.

As far as turning a wooden bookcase into a rack....I would be much more worried about the humidity of BP tubs than the heat. What kind of wood is it? Is it polyurethaned or treated in any way? Is it a nice heavy duty bookcase or a crappy particle board one? All of these factors will determine if it can work as a good rack.