This site should make it easier for you to find the sheds available for your bike or bicycle.
Of course if you've got a bit of space in your garden shed, then bicycles may well fit in. However, trying to move a bike around or extract it from that sort of environment regularly will be very frustrating, unless everybody is extremely tidy with all the other things that can find themselves in a garden shed. Also garden sheds are very insecure especially with bike theft increasingly common.
If you don't have a shed or garage then there is always the option of storing your bike in the house or flat. If there is space and you live alone, that's not a bad solution, unless you indulge in muddy mountain biking, when you might need a maid to clear up the mess after you.
Finally some places where you might want to leave bikes just don't have the space or security; for example caravans and mobile homes. Fortunately quite a few bike sheds will fit neatly under a caravan window.
Security is also much higher for several reasons. Firstly custom-made bike sheds and stores don't have any windows, so potential thieves can't see whether bikes are inside, what type they are or what value they have. Also, particularly with metal sheds, specific reinforcements are included to make breaking in extremely difficult.
Some of the top sheds are highly rated in reviews and a few have certifications for resistance to damage and recommendations from the police and other interested parties. In particular this applies to the metal sheds from Trimetals and Asgard.