Buying a shed that's too small is the most common mistake backyard owners make. Before you order, make a list of everything you plan to store: a lawn mower needs roughly 3x2 ft, bikes about 6x2 ft each, and garden tools need wall space more than floor space.
As a rule of thumb, a 4x6 shed suits tools and bikes, an 8x8 handles a mower plus seasonal gear, and anything 10x10 or larger works as a small workshop. Leave at least 20% free space for the things you'll buy later — you always do.
Also check your local regulations: many areas allow sheds under 100 sq ft without a permit, which is why 8x12 models are so popular.