tickets for outside courts

I would like to visit the french open over the middle weekend and I'm interested in doubles and mixed so I would love to visit the outside courts.
how much is it for students and can I buy outside court tickets at the local office or do I have to order them in the internet?
thank you! :)

nobody can give an advice?

http://www.fft.fr/rolandgarros/billetterie_en/

i think you will find everything you need here...