i've been reading... no.1 shed is a concrete garage with a plywood + felt roof. above the roof is a second roof, made of steel profile supported on scaffolding boards. there are no metal rafters, or frames, or any way of touching the steel from inside. i'm intending to run a 32A supply from a separate CU into the shed using 6mm 3core SWA - a distance of around 10m altogether. however, upon reading, it looks like i need to bond to earth any "extraneous conductive parts" using 10mm copper cable. so... is the steel roof an "extraneous conductive part"? what about a planned 22mm copper line from the air compressor in a separate (all timber) shed? should i just go for 10mm² swa cable anyway? tn-c-s earth to the house, btw.