Forget the lot use thermoboard, which is plasterboard with 30/40/50 mm
insulation bonded. £17 an 8x4 sheet fix with drywall adhesive.£4.75 a
25kg bag. Bingo finish in one.

For a shed, though, it might be more appropriate to use plywood instead of
(or in addition to) plasterboard, as it is much easier to fix shelving and
racking to.

Christian.