Like the Smart, the A2 is a novel design with much to recommend it.
If you are buying a 1 year old example the few glitches which affected the build on earlier cars (driveshaft noise for example)will be avoided. You will also benefit from design improvements to fuel tank size, windscreen wiper etc.
If a "UK"car it will have the balance of the 3 year/60,000 mile warranty provided it has been serviced by an Audi dealer.
Variable servicing intervals can mean lengthy spells between workshop visits - check how long your potential purchase has to go to it's next service by pressing the left hand button within the instrument cluster with the ignition on.
In my experience A2's are built to exacting standards - any uneven panel gaps or suspect paint should put you on guard. Be aware that the aluminium spaceframe needs specialist attention if involved in a collision. If damaged, any repair undetaken by an authorised repairer should be anotated in the body repair section of the car's service book.
A common complaint is that of interior rattles and squeaks, maladies made worse by the car's stiff suspension. Always have a lengthy test drive in any prospective buy.
Good luck!!
Regards
Ian - 2004 1.4 Tdi 90 SE, prev 2001 1.4 SE