Jim, an interior finished dimension of about 4'6" X 4'6" is needed to accomodate 30" for a toilet and 24" for a vanity, side by side, with the door opening in front of either fixture.
If you use a pocket door or an outswing door and put the fixtures opposite each other with the door opening between them you'll need an interior dimension of 30" wide X 6' long.
Any smaller starts requiring unusual fixtures and a steady diet of Slim-Fast. Good luck!
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