A ridge plate is usually the very peak of the garage The pointed part of the garage whether it's a Hip four-sided garage or a Gable roof two-sided garage. Either way both of these roofs can get a little sag or big sag overtime. The reason for this is because they are either no upper collar ties or lower wall ties which keep the roof in the walls in place. The upper collar ties usually sit below the Ridgeline the pointed part of the roof usually two feet to 3 ft down. Also there are wall ties that go from top plate to top plate these keep the walls from spreading apart I've been in jobs were a lot of guys did install garage doors they'll come in and cut them thinking they did justice by putting a new garage door in and they actually destroyed the garage because I've had to repair so many garages because they decided to cut the collar ties 50% of the time and not reinstall them right above the garage door they would have did that the garage walls what have never bought out in a roof would never came down with a sag so I usually want to do a garage repair I usually check to see if there are collar ties in wall ties most the time there's not so I jack the walls up I pull the walls in and I install them and they're good to go 100% of the time