You will need 9 buttons. Rowan used # 9427230100 by Groves and Banks in the UK.

Finished measurements:
Bust circumference: 44.5(48, 52, 56, 600” 113 (122, 132, 142, 1520 cm.
Finished Length: 32(32.5, 33.5, 34, 34.5) “ 81(83, 85, 86.5, 87.5) cm
Sleeve to underam: 17(17, 17.5, 17.5, 175)” 43(43, 44, 44, 44) cm

Yarn used:
Rowan Alpaca Classic - yarn held double
Feather Grey Melange 101 - 27(30, 33, 35, 38) balls