it depends what engine size you're interested in. let me know what engine you want and i'll tell you what specific issues that engine has.
faults that are common on all models include (use to get price down if you find them):
-door handle rubber persihes
-rear wash doest work (due to blocked non-return valve or pipe come off in tailgate)
-rear wiper doest work (due to rear wash pipe leaking on it)
-sunroof leaks (look for water marks or mould under sun visors)
-anti roll bar drop links make knocking nosie voer rough surfaces
-door check strap bracket snapped (door swings freely or makes loud clicking noise when opened)
-stalk switch assembly faults (check all lights and wipers work correctly)
-instrument panel faults (check all gauges work correctly)
things to check for on all models include (can also be used to get price down):
-red key (master and cant be replaced)
-2 blue keys (with working remotes on higher spec models)
-2 alarm keys (on mk1 models that have an alarm)
-2 remote key code keyrings (paper keyrings with 4 digit codes, only on mk1 models with remote keys)
-timing belt change at 50-60k (costs a lot on 2.0 models)
-air bag light comes on for a couple of secs when starting engine and then goes off
-abs light (comes on & goes off same as airbag light) on models with abs
-check fuel injection system fault light goes out, same as airbag light
and the most important rule to remember, never buy a 1.4
(no offense to the 1.4 owners, but you know its true)