I had a Renault Scenic and you had to buy the specific Renault fitting sliding, lockable bars. It then depends on what you want to carry - but look at a roof box as it fits with the roof bars better than a roof rack, boxes are lockable and covered and are practically better.
A roof rack is usually a square/oblong fixed frame, attached to gutters on a car. I havent seen one for years.
A set of roof bars are a more modern alternative which simply fix horizontally accross the roof so that things such as ladders and roof boxes can be attached to them.