1) A round-headed nail made by blacksmiths (OED).
Examples in the OED are given under ‘brad’ which is defined there as a thin, flattish nail of the same thickness throughout but tapering in width, having a small ‘lip’ on one edge, instead of a head. The evidence makes it clear that it could be used in roofing: 1309 pro iiijML broddis emptis iiijs viijd, Bolton Priory
1371 Et in m. brods emptis pro domo scolarium cooperienda, 18d, York
1399 240 broddis, Selby
1444 pro v.m broddes, 7s, York
1548 ij.m broddes, 2s 6d, York
1559 A thowsande broddes, 20d, York.