I spent most of last summer doing a workshop for myself and also a play house on the other side of the garden for the kids. My work shop is fully insulated with inner and outer walls filled with rock wool (it gets pretty cold here in winter) double glazing on the windows, solar powered outside lighting, full electricity with lighting and power outlets inside, insulated flooring and fully painted inside and out with an acylic based all whether paint. It's pretty cosy. :-)