Yes itcan be hard to find the leak.
Check the drain holes in the area of the pollen filter. They should drain any rain water away, maybe blocked.
If the windscreen was replaced double check around the seal. You may have to take the internal trim off around the screen to do this.
Sometimes lifting the carpet can also help, you wont get mush room but you may see where its coming in.
We had a leak that was coming in through the door light switch, took awhile to find that one.
Have you a sunroof?
Newspaper under the slip mats will help with the cleanup, just keep changing until dry.