I have a garage on the end of a pitch-roofed bungalow which I would like to make into a work shop. The roof is of purlin and rafter construction and there are only three ceiling joists across the 3.5m width of the garage, one at each side by the walls and one in the middle. Ultimately I would like to put a proper insulated floor in above for storage but for now I want a cheap and cheerful way of blocking off the roof void above these joists. I will be putting vinyl on the (uninsulated) concrete floor and making up a frame around the garage door and filling the opening with some spare 100mm Kingspan. I am thinking about tacking some bubble wrap on top of the joists which should stop draughts from the uninsulated roof void and provide some small amount of insulation as a temporary measure for this winter. The garage houses the oil boiler. Any comments from more experienced DIYers would be welcome! Thanks.