Old felt roofs
Look for splits at laps, blisters, lifted perimeter edges and ponding. If the deck is soft underfoot, the covering may no longer be the only problem.
Pitched garage roofs
A tiled or slated garage roof can have the same faults as the house: slipped coverings, ridge problems, damaged felt and failed flashings. Because garages are lower, wind-driven rain around side abutments can be more noticeable.
Older sheet roofs
Some garages still have older corrugated sheet materials. Do not drill, cut or disturb a sheet you suspect may contain asbestos. Identification and safe handling matter more than getting a quick patch on it.
Keep stored belongings in mind
A small leak can damage tools, boxes and electrical equipment long before the structure looks serious. Moving items clear of the drip is a sensible first step while the roof is being assessed.