There currently is one option to travel by night train from Paris (France) to Rodez (France), taking between approximately 11 and 12 hours: Namely the INTERCITES DE NUIT n° 3755 operated by SNCF.
In France, a few night train lines are operated by the state-owned SNCF.
In their night trains, they typically offer two types of carriages: seats and couchettes, with the latter available in first and second class.
In the couchette carriages, you travel in 4-person compartments (first class) or 6-person compartments (second class). The berths are simply designed in both classes and are about 1.9 meters long.
Yes, they are available. You can book an entire couchette compartment for private use. This can also be done for a group.
First class berths are slightly wider than in second class and there are only four berths per compartment. Advantage of first class: In Paris and Toulouse, there are showers at the stations for first class passengers. In second class, six travelers share each compartment. For cyclists, it's possible to bring a bicycle in second class for an additional fee of 10 euros.
You should bring your own food as there is no restaurant on board. Alternatively, you can pre-order meals and drinks or eat before departure. First class travelers receive a small breakfast. Each passenger receives a night kit with refreshing towelette, dental cleaning tablet, sleep mask, earplugs, and water.