I would suggest a russian tortoise. They are small enough to live comfortably in the enclosure size you stated, are very active and personable, albeit not the prettiest tortoise. They are readily available and not uber expensive. They are pretty hardy and temperature tolerant as long as they dont get wet or damp when temps drop below a certain point. I leave mine outdoors here in Louisiana until the night time temps get around 55 degrees F. I take them in at that time mainly due to the wet winters here, and cool and wet do not mix well with most torts. A word of caution, the do dig!!! If put in a pen outdoors, make sure the bottom of the pen walls are buried at least six inches or so, or place screen on the bottom of the pen and cover with several inches of substrate.

Good luck!!