How old of a Saab 900? I used to own Saabs, and I also sold them for a while. The original Saab 900 is a great car, quirky (such as the ignition being between the front seats and having to lock it in reverse before you can remove the ignition key) and fun to drive. The cars made under the ownership of GM have lost that edge, becoming more "bland" and generic as a result. Still not a bad car, but pricey!
If you are going for a convertible, 1993 or older, then you will not be disappointed. I drove one for a while, and loved it. The roof is snug in bad weather (drove it home through a blizzard, not a leak or a drip) and the glass rear window with de-fogger is a nice touch. Great in snow with the right tyres of course. Refinements such as heated front seats and fog lamps really help in bad weather too. The roof is power-operated, and works well.
A few things to bear in mind, the leather can be a little fragile, but I think that you can get replacement seat covers still from the aftermarket. Transmissions can be troublesome, but a lot depends on how they were treated of course. If you get a non-turbo car, then go for manual shift, the automatics are reliable, but dog-slow and only three ratios. Turbo with the automatic is fine, but with a five-speed stick shift is a hoot! The car is strong and safe, assuming no rust, and I have yet to see a rusty convertible! The covertible was designed as such from the ground up, so there was never any scuttle-shake when they were new, as opposed to cars such as the BMW convertibles of the same era.
I actually sold a turbo convertible with five-speed to a guy I know who still has it, twelve years old now and 170,000 miles later. It has been stone reliable, and he swears he will never part with it. Mind you, he has been meticulous about its upkeep and maintenance, and it still looks like a new car! Look for one with a service history and evidence of having been loved and you will not go far wrong.
Sorry to drone on a little, but I do love these cars.