I have modelled it on the cabin Captain Scott built for himself when over wintering in the Arctic prior to his attempt on the North Pole. Although his was part of a larger shed it's true to what he sought with a bed, desk and book case. It can as a result, be slept in, but is mostly used for reading, planning adventures and snoozing. There is an electric heater (designed to look like a stove) & it is very well insulated, so can be used year round.
It had to be squeezed into a space with brick walls on three sides and on a base that is two steps up, on a platform fronted by a brick wall. The dimensions meant we couldn't buy an off the shelf shed, but had to make the four sides and roof as separate components & build it into the space.