It's really a question of having things out of sight. I honestly wonder if it's better to look like you don't have much worth stealing to begin with. Your bike being out of sight with a flimsy padlock is enough to deter 99.5% of all would-be thieves. Locks make good men honest.
If you had something like a
shed shackle or ground anchor that meant a would-be thief needed an angle grinder to get your bike, they've already self-selected themselves as part of the 0.5% who would break into a padlocked shed.
A thief will get into any shed of any manner of construction. It may be marginally harder to break into a steel shed, but if you have the determination (and a battery powered angle grider) there is no way for me to stop you. I really do wish people wouldn't talk about Asgard sheds being some sort of magic bullet that will make it impossible to steal your bike. It isn't true.