The roof protects the garage
It’s easier and more economical to make a flat roof with a slope of several degrees. For the Middle Strip, the minimum slope is 8 °, but it is better to at least 10-12 ° - the snow comes down better.
In the case of a freestanding garage, the front wall is made higher and all sediments flow / fall back. This must be borne in mind and not put there any items, do not place buildings. If the garage is attached to the wall of an existing building, the slope is made to the side of the house.
Minus shed roof for the garage - no attic. Pros - a simple device and low cost. Another positive point concerns the improvements: then it will be possible to build an attic floor above the garage.
The gable roof is more difficult to implement: it requires assembly of the roof system and roofing material is more. But - there is an attic and the appearance is more "civil".
Quite often you can see the attic floor above the garage. The room can be used as a guest house. The cost of arranging the attic, more than the construction of a conventional dual-slope roof, but additionally it turns out still a decent area.