I work in an “Eco Space”.
It was constructed in the UK under strick ecological principals. It has 250mm insulation on the walls and 300mm on the floor, a roof planted with sedum, a grass look alike, not only it does not have a visual impact in the garden but the soil in the roof acts as insulation.
The exterior walls are cedar wood and the interior floor is rubber, it works great with the under floor heating.
It took four days to erect on a base constructed by us here.
I am very fortunate to be able to see the changes in the garden as the seasons pass. Every day there is a different interest.