When planning for your garden room, location and size are key considerations. In most instances planning permission is not required. However, projects are required to be constructed under permitted development rules, which amongst other things can limit the size of your garden pod.
What Can I do Under Permitted Development?
Thankfully you can build up to 15m2 (internal area) within 1m of your boundary, or up to 30m2 (internal area) when 1m away from your boundary.
Your garden room should be single-storey with a maximum eaves height of 2.5 metres. For dual pitched roofs this increases to four metres or three metres for any other roof.
If you are erecting a garden studio within two metres of a boundary, the maximum height you can go to is 2.5m.
It‘s important to remember that no more than half the area of land around the "original house" should be covered by your proposed garden room project.
If you want to learn more about planning permission and permitted development rules, the planning portal has some really good information. https://www.planningportal.co.uk/info/200130/common_projects/43/outbuildings
If you’re in doubt you can always speak to your local authority planning office for further advice.