You've probably already done this, but - if not - try a Google search using "oldest man-made structure". You'll be offered over 1200 sites and - looking just at the first page or two - there is a whole raft of contenders including the idea that an under-ice anomaly in Antarctica might be something man-made!
Depends on your definition. Do you mean �still standing today� or just archaeological evidence of the oldest �man made / artificial� structure found? If the latter then it could be Terra Amata in France, or the shelter at Chichibu near Tokyo.
Many thanks everyone. With global warming I don't expect Frosty the Snowman to be around much longer ! The pub brains trust didn't specify whether the structure should still exist or not but I shall report back to it at our next Real Ale soaked meeting.
Into which category does your shed belong, horsestache 1 ?