Wait what? If I remember correctly when you buy a California it's without roof, but when driving it's always has a roof! Can you post a GT5 pic of a Ferrari California without roof?
To show that I'm a nice guy, I'll put my GT6 download on pause for you so you can see for yourself. Apologies for the poor quality.
I think if you go on a track with weather change it'll automatically go up. Or, you put a spoiler on it.
Thanks guys! I think they changed it, because I've tried it only in very first versions (and after disappointment never tried again), and I certainly remember I've tried California at Fuji. Anyway It's fixed now!