Roof/Truss remodel

Currently we have a flat roof that has been causing a leak because of water damming from winter and sideways rain. I have been talking with some people about re-engineering my roof so that it won’t leak. My main thought is adding lumber to the existing trusses over the garage and running to a wall on an addition that was built in the past. However I am not sure whether that would be acceptable and I don’t know enough to understand load or other factors that could be involved. I know in my idea that I would create a new valley coming off of my main roof line and creating a half gable sort of thing on the other side.