Climate controlled garage would be a lot better, especially since the car is a ragtop. Storing a car during in general is not really a good idea. Cars simply are machines, and bad things happen when these machines don't get any use for a while, plus your car just sits there and depreciates in value while it isn't even getting any use. If you must store the car, make sure you take the proper precautions. Fill the tank up to the top with gas, put in some fuel stabilizer, remove the spark plugs or spray them with a special "preserver" type lube, among other things.
There is actually a proper way to store a car and I think it would be a good idea to find out what that is. Definitely go with the climate controlled garage, though....I'm assuming it's a bigger investment, but I think it is well worth it.