Internal & External Sizing
The chart below gives you the external dimensions for the Groovy Garden Room you want.
To get an idea of the internal dimensions, all you need to do is subtract 133mm which is the nominal thickness for each wall.
Planning Permission
In terms of whether or not you need planning permission, then the rough rule of thumb is that any garden room that is more than 30 sq m of internal space will need approval from your local authority. If it's under this, then you're unlikely to need planning permission under the Permitted Development rules.
But we advise that you check with your Local Planning Authority.
Then you can work out the perfect size for the plot on which you want us to install one of our Garden Rooms...