There are two or three things that could cause this. Put kitchen roll across the dashboard and below the sun roof. Turn a hose on the car for 15minutes and take a look inside. If paper is absolutely soaked, repeat but for a shorter time until you identify the source. The other likely fault will require looking under the bonnet. If you look near the wiper mechanism, there are small well areas on each side that have a drain tube at the bottom. If the tube is blocked, water will flow around the pipe and into the car. The most likely thing is one of these drain tubes is split, or has come off. This is not the easiest piece to fix, but if you are confident removing other parts for access it is cheap.
Answers & Comments
There are two or three things that could cause this. Put kitchen roll across the dashboard and below the sun roof. Turn a hose on the car for 15minutes and take a look inside. If paper is absolutely soaked, repeat but for a shorter time until you identify the source. The other likely fault will require looking under the bonnet. If you look near the wiper mechanism, there are small well areas on each side that have a drain tube at the bottom. If the tube is blocked, water will flow around the pipe and into the car. The most likely thing is one of these drain tubes is split, or has come off. This is not the easiest piece to fix, but if you are confident removing other parts for access it is cheap.
I would have the windshield checked for leakage.