OUrs is just the shed. It has power, lighting, worktop, shelving and windows, but the walls are unfinished on the inside. Calling it anything else would imply, to me anyway, that it is nicely furnished as well.
George Bernard Shaw had a writing hut. I went to see it recently. It is tiny. But quite spectacular in that it revolves so that GBS was able to always benefit from the sun. It had a bed and a desk in it. I suspect Mrs GBS sent him in there when he'd gorn over the top on the alcohol.
I also saw recently that Louis de Bernieres also writes in a writing hut in the grounds of his house on the Suffolk/Norfolk borders.