Very common problem mate
Mine did exactly the same at first. This is what i did:
1. The external plastic trim that goes around the sunroof on the roof, i prised the edge up and ran a bead of gutter sealant all the way round, then wiped the excess off leaving a nice seal all the way round.
2. Removed, cleaned and greased the external sealing strip. If you open the sunroof and look at the recess between the glass and plastic trim, get a flat screwdriver (be careful not to cut it!) and prise the thin strip out of the aperture, this strip is crucial to water tightness on the sunroof. I was going to replace it but Renault want £100 for a new one!!! Therefore i thoroughly cleaned it, greased it up and replaced.
The 2 above should sought it as these are the only places the water can get in.
Good luck
Just an afterthought, dont rule out the sealant around the aerial, as this is also a common area for water getting into the cabin. I removed mine and applied a layer of sealant. Dont tighten the aerial up to much as all this is push the sealant straight out of joint.
