The 99 and later were pretty well sorted.
As above operate the roof several times with both soft top and hard top (a fairly loud bang as it releases the roof is pretty normal).
Check plastic window condition.
Check the roll over bar operates correctly. Check it has the hard top included (they all came from the factory with one so it should be included). Check it has the rear wind deflector (again included from the factory but often missing and sold for silly money by the previous owner). If it has ADS operate the system through all height settings several times (proper gangsta!).
Check all the cubbys unlock and lock correctly - including door pockets (you might not even know they are there but lift the armrest top), centre console locks, sun glasses compartment, and the two roll top compartments should all lock with the central locking. Check the heater vents all operate correctly - they are driven by vacuum and the vacuum manifold under the bonnet and vacuum lines can give trouble sometimes - easily sorted but a bargaining point. Vacuum actuators can also go bad which can be awkward to get to. When locking and unlocking the vacuum pump in the boot should only run for a few seconds. Any more and it may have a vacuum leak somewhere. Check the condition of the fuel filler seal (under the filler flap) - they deteriorate and can leak water into the boot - it falls onto the vacuum pump and destroys it (pumps are around £400 used - no longer available new). Check both sides of the boot for water ingress - the aerial rubber seal also deteriorates and leaks water into the boot. The aerial should work as well (also no longer available new and stupidly expensive used).
Check the condition of the top strut mounts - any cracking at all and they will need changing (not expensive or difficult). Check for broken springs and check for rust around the rear subframe mounts (can be hard to see) and on the sills especially around the jacking points.
Engine (M113) is bulletproof and rarely gives issues as is the gearbox (722.6) which has only an electroplate issue which sometimes rears its head (around £400 if done by an indy). Back axles is again pretty bullet proof.