Roofing

I have an attached room addition that was a garage. The roof leaks that's attached to the room(between the house and the room) on porch causing water to go up under the french doors of the room, resulting in flooding the inside of room. The last contractor did not finish repairing it properly. The roof is made of tin, and the seams from his last job has water going under seams coming through the small nails in the tin roof. So porch fills with standing water and has no other place to go but under the doors to the attached room. I may need a drain system on the porch area.