It really depends on how big your studio is, but generally you'll need perimeter rails all around the edge and load-bearing rails spaced about 60cm apart in both directions. For a small studio in Marseille, I'd say a pro might ask you for maybe 30-40 meters total, but you really gotta measure your space first. It's not super complicated if you're careful, but it's a pain to do alone - the rails are long and awkward to handle, and it's gotta be perfectly level or you'll see it right away. I'd advise you to call someone to at least check the mounting points, especially if you've got old water pipes up there.