Good repair person needed for rain leaks in house

Can anyone recommend a good repair person or company that is good at tracking down rain leaks in a house, running down wall and coming out at the window areas? This room is under a flat roof, used as a deck.

Anyone familiar with coatings used to seal out rain on top of rooms with flat roofs, that is also used as a deck? Products best to use? Who can reliably install and stand behind their work?

Thanks!