Bought about £150 quids worth of screws, nails, brackets etc from screwfix and iron mongery direct.
Bought a breather membrane off eBay £60. 1.5x50m so should get the whole thing wrapped externally in 1 roll.
Bought a thicker insulated foil backed type of stuff for internally prior to boarding it out. The stuff you see marketed for lofts. Not sure if it will add anything to the build but we’ll see