If you have a flat roof with an up-and over door, there’s nothing to be done. The scum hang on the roof and kick the top of the door in making those garage-door t-handles you see bolted to floor pointless. If the bottom is uncovered, you can hook something underneath and rip the door down. If the top is uncovered you can jam a screwdriver/knife and push the sprung-loaded bolt down. Some of the door locks are easy to pick.
The last 2 I learnt as a kid to get into my dad’s/friends parents garage to get our bikes out when our parents were away with the keys.
If you armour the door with bolts, they go in through the roof, and dismantle the door from the rear. A neighbour had his 2 Gas-Gas trials bikes stolen exactly that way.