Does anyone have any experience getting a roof box for a brava?

Im new to this, but how does it attach to the car?

Yes, thule do the best one in my opinion, i own quite a few sets, and use them with the different foot packs on all my cars, even with a huge roofbox at autobahn speeds there's been no problem. Or bikes, or cannoes, or ladders or kayaks.

It attaches by little feet which grab hold off the roof under the doors, there molded to the car so you then can shut the door etc etc, dont get a generic one they're likely not to be as secure and could damage your door.

Do you know what the attachment pack is for use with a Brava?

A 5 second check of www.thule.co.uk shows
120cm bars (761)
feet (750)
rapid fitting kit (1059).