When I had the shop rebuilt I asked the builder to specify some hefty insulation. The problem in the old shop was it had an asbestos cement paneled roof. This let in the heat of the summer and the cold of winter and meant it was not comfortable when it got too hot or cold.
I have great joy to report that the layers of solid hard form insulation he used have left the temperature in the shop at comfortable levels.
Yesterday Sunday 7th July temperatures outside reached 30 Celsius (86 Farenheit) and the temperature inside was a very cool 20 Celsuis (68 Farenheit)
I am one happy woodworker.