Leaking Buick

2003 Buick Cent. leaks on passenger side floor when it rains. had a Skylark that leaked also. HELP!!

Create your own rain. Have someone (the “perp”) play a garden hose sprayer over the car as you stay in the car and look up under the dash. You may be able to determine where the water is coming in.
An auto body repair shop would be your best shop for this problem.