Hi poorman and welcome to RenaultForums...
The problem with leaking Scenics is a known issue. It is generally due to a blocked or kinked drainage pipe. I think this comes out of the car near the passenger front wheel arch. You can attempt to cure it from the sunroof end. If you open the sunroof up you should be able to find the drain holes. Find a cable or other flexible, long object that is smaller than the drain hole and try to feed it down. If it is blocked this might solve the problem. A small amount of water poured down each drain hole should result in a bit of water behind the front wheels
If the problem is restricted to the rear, it could also be that a rear bulb has been changed and the lens or cover not fitted correctly. Might be worth checking too
You have my sympathies by the way. On my R5 GT
I had an after-fit sunroof which leaked. Being afterfit I don't think there were any drain holes. Water used to fill the sunroof cavity to the brim and pour over me and the missus at the first corner!