Good choice. A lot of people I've spoken with rate the 1.8 over the 2.0
Make sure the cambelt, tensioners, pulleys and variator were done at 36,000 or will be done as part of the deal. Check the condition of the water pump too. If there is any white/blue residue anywhere on the pump it needs changing. Even if the belt was done recently, if the pump is worn you can still throw the belt and say ta-ta to 8 spark plugs, 16 valves and a whole load of oil as your car grinds to a spectacularly noisy halt. Many is the car owner (this is NOT an Alfa problem, it's a timing belt problem) who has had a belt changed only to have a tensioner or water pump fail.
Check for knocking from the suspension (a couple of speed ramps or just bumpy roads at low speed will let you know on this one). If the knocking is at the rear it will the trailing arm bushes. £3.00 each, but about 45-60 minutes labour each side as you really need to get the rear discs off to work on them. If it's the front it will most likely be the wishbones. Bit more work involved there.
Final point is oil. These engines can go through a litre in as little as 1,000 miles. If there is any sign of oil starvation (dipstick, noisy valve gear, rumble from big-end) walk away. As soon as you are out of sight break in to a run and keep going. Change your identity and move to another town if you have to, but don't buy the car!
Remember that many people sell their cars shortly after
paying out a small fortune on repairs. There's a good chance that the above have already been dealt with, leaving the previous owner with a large bill and a nasty taste. You get to reap the rewards.
Just watch for the main points above and make sure you get a reasonable warranty.