| I'm just in the process of doing this myself. We bought our convertable about 4-5 weeks ago and its blue roof looks like it has never been cleaned!
After a lot of research I have decided to use RAGGTOPP Cleaner and RAGGTOPP Protectant which is recommended by the Haartz Corporation who are the supplier of convertible topping fabric for virtually every U.S. manufacturer and most European manufacturers.
I gave the roof two goes with the cleaner this afternoon and you should have seen the dirt come out!. Tomorrow morning I plan to do one more clean and then once dry apply the protectant. | 
