Goldeneaglepilot is right - it gets VERY busy; slots in and out have to be pre-booked and as he says if you miss one you can be flying around, or waiting on the ground for a long time. I know of a number of people who have tried to get slots but failed as they wanted to stay, and there was insufficient parking space.
Furthermore, the landing fees for that weekend are very high - even in British terms! . There's a very good and cheap alternate - Laval - cheap landing fees and parking and cheap car rental. Customs used to be OK but not sure if they are still there after the latest cuts in France. I've been to the race a number of times using Laval, but not for about eight years.