I jut fixed this last weekend on my wife's car. There are four drain holes on the sunroof- one from each corner. The front left and right drains run down the front left and right columns and into a rubber fitting that carries the water into the front quarter panels to drain. When the rubber fitting gets clogged with gunk the water backs up into the passenger compartment and floods the floor mat. The fix is easy- under the grab handle are two bolts that hold the plastic column cover on- unscrew the bolts, firmly pull the plastic piece off and expose the drain tube. pull the tube out of the rubber fitting, pull the fitting and clean. you can also run a wire down the tube from the sunroof- but be careful it is does not puncture the tubing. This should solve your problem. To test pour water into the sunroof drain and verify it flow freely out from under the four quarter pane(s.