You get the full flat if you are in grade 6 and above. For grade 4-5, you share the flat with other staffs. Normally there are 2-3 bedroom flats.
But if you are grade 3 and below, you share not only the flat but also your room. Minimum 2 in one room (depends on the size of the room).

I got this information from this thread http://www.qatarliving.com/node/157528

Hope I helped :)

Have a nice day

Cheers