The point where a shed stops being about lawnmower storage is usually late summer, when the evenings are still warm enough to sit out but the light's going earlier, and you realize you want somewhere to retreat to that isn't the kitchen table covered in mail. That's when people start looking at these not as a place to dump the mower but as an actual room, just one that happens to be outside.
If you've never owned one, start plain and small. A basic outdoor shed, timber or metal, no windows you haven't thought through, nothing with a pitched roof that's going to eat half your budget on looks alone. You can always add shelving and insulation later, but you can't easily shrink a structure that turns out too big for the plot. Where it goes wrong is right up against a fence line or under a tree that drops sap and leaves on the roof all autumn, you want a gap for airflow and somewhere you can actually walk around it for maintenance. A cheap metal shed in full sun will tick and groan all day like it's complaining about the heat, and the paint on the bad ones chalks off on your hands within a year. The better ones have a proper coated finish that just gets quietly ignored by the weather, which is all you want from a shed, honestly. On color, go neutral, a soft gray, a muted green, something close to the planting around it rather than bright white that'll show every streak of dirt by spring. For a studio or garden room, the same rule applies tenfold since you're looking at it from indoors all winter, and a loud color you loved in the showroom gets tiring fast when it's the view from your kitchen window every single day.
Measuring up matters more than people think, and not just for the footprint. Measure the access route from the street or side gate, because a large shed that fits the garden beautifully but can't get through a side passage is a very expensive mistake someone's making this week. Measure the inside with actual furniture or equipment in mind, not just floor area, since a bike, a workbench and a mower will eat a small shed's usable space faster than you'd think. And check headroom at the eaves, not just the ridge, because that's where you'll be reaching for shelves. Buy one size up from what feels necessary, you will fill it.
A good shed earns more goodwill in a garden than almost anything else you can put back there.