If...you have a sunroof, and the drain ports are plugged that leads away from the roof gallery, then the water will drain down the trim, along the windows and end up on the floor. You could also have a loose fitting window, that might lead to a similar condition. Additionally, if the rubber tube used to direct the water from the sunroof is broken half way down, it will also leave things damp.
It could also be leakage around the roof rack.
JP