Ah ok, so you're looking pre-facelift right?
So that's the M54 engine, chain driven, belts are technically an inspection 2 item, so should be done every 4 years-ish, however, don't let that put you off like it does in the Clio. You can change them yourself very easily, no timing involved, they're just aux drive belts. It took me and Ant about 20 minutes to change them both.
Things to check wise:
Oil leaks - Rocker cover and oil filter housing are quite common (not expensive to fix)
Knocks and bangs - lower arm bushes, or prop shaft donut (not expensive to fix)
Clutch is a bit of a pig of a job, so try to make sure that what you buy has a bit of life left in it!
Roof operation - I'd almost say if you can find one with a fucked roof and buy is super cheap, do it! I had my roof out and got it working for 1 day of Giraffe and myself f**king around and about £8 in parts
So, then the big thing is spec, spec basically makes of breaks the car (IMO).
The big thing is to make sure you get the sports seats, standard seats look waff, and are largely flat, so don't hold you in. Heated preferably too
Then you're looking for xenons, cruise, the screen in the dash if you're lucky (just improves the interface and tells you more about what's going on)
Feel free to send me a link of anything you're looking at and I'll give you a whistle stop assessment.