The Metro is very easy, and will drop you off just a short walk to Roland Garros. My wife and I had a magical time last year in Paris. We rented an apartment for the week in the 1st Arrondissement, right next to a huge market.
By the Gare Du Lyon. There's a hotel there called the Mercury and it's a 3* hotel and a reasonable price. Also being at the train station, there are metro trains going to the Roland Garros area every 15mins!
I did this last year......GREAT!
Hotel Relais Bosquet in the 7th was great. Spent a week there.. very convenient to many sites and right on the Metro line at the l'Ecole Militaire stop. I wouldn't recommend booking your room based on proximity to Rolland Garros unless you are elderly or playing in the tournament. The metro is so easy and quick. PM me if you need a tour guide. I'll do it in trade for air travel, room and board and two tickets to the tournament.
try to find an apt. for rent...much cheaper (& more fun) than a hotel...public transportation is GREAT, and just take a metro to RG (easy access) personally, i like to stay in the Marais, lots of charm, cobble stone st,...