A standard-sized single garage is ideal if you are looking to create a home office, playroom or guest bedroom with en-suite with your garage conversion — or even a downstairs bathroom or shower room and a utility. It would give you around 14m² of extra space, so you may also be able to fully knock through the walls and extend into an existing kitchen or lounge for instance.
A double garage offers many options for conversions due to the 28m² of space it creates. It even allows to keep part storage and part living space.