All these different types of insulation, I see the thin aluminium foil type and the thick wolly type.
Do they all need to follow the roof gradient (more meterage) or can they be laid flat above the ceiling (less meterage)
Which type cheaper ?!?

All the option presented here seemd to take a lot of work. What about the whirlybird thingy (the spinning mushroom) option.
Is it good for residential house?