The garage roof is the main part of the garage whether the garage is new or old. The garage roof if not proper can pose problems with the authorities and also you can encounter leak in the roof and spoil all the stuff kept in the garage.
The roof should be such that it keeps the rainfall from accumulating on the roof thus leaking into the garage. The roof should have a slope so that all the rainwater falls down instead of making a pool on the roof.
Roof drains and edges should be installed for the water to fall down directly into the sewerage. The flat roof almost always will leak and especially when it is raining or when the roof is old.
The roof need to be of solid material and should be installed taking the weather in your area . If you stay near the coast where there are heavy winds your roof need to secure the roof more strongly. And proper slope should be given to the roof tops.