I've just insulated and boarded out a 3m x 5m metal shed with wood battens, 25mm Celotex in the spaces and all the insulation joints foil taped prior to boarding out with 18mm OSB.
I'll report back on heating requirements once it gets icy, meanwhile I've fitted an extractor as at the moment it gets too warm for jeans & T-shirt sat at the bench with just me & the strip lights on ;-)

- Nick