New home, new problem. After our first rainfall, we noticed a large puddle of water near the corner where the garage meets the house. An electrical contractor on site tells me there is a leak between the garage (an add on structure) and the house, and recommended calling in a roofer. I took a look and see no metal flashing in place between the structures. Is installation of flashing in order here? If so, is it that hard that I need to call a pro? I'm moderately handy, and think I can handle it if that's all that's needed. Thanks!