How big should my home studio be?

I frequently see people who are remodeling their house and want to create a proper photo studio as part of that space.  Since space is almost always at a premium during a home remodel, these folks want to know how small a space they can get away with allocating to their studio without making it so small that it's not really usable.  Of course, the answer depends on what type of subjects you're photographing:  automobiles require more space than jewelry.  However, by breaking it down and adding up the space required for each individual component, it's not hard to come up with a number that serves your needs.