Renting space is an allowable expense - e.g. renting a desk at WeWork or access to a pottery studio. Creating new space usually cannot be expensed.
If you rent an office or a space to work in (for you business) you can expense it.
Buying additional space is more complex, but in the majority of cases the cost should not be expensed.
Structures, such as a new shed or extension can't be expensed by a sole trader, this includes the design, delivery and associated labour.
The fit-out of that shed or extension with fixtures and fittings specific to your business can be expensed. That includes any fittings and the associated labour required to ready the space for work. That said, any spend that adds value to your home, should not be expensed.