You will need 6 buttons. Sirdar used their buttons #B5611-0785.
You will also need stitch holders.

Finished measurements:
Chest circumference: 39.5(43.25, 47.75, 51.5, 55.5, 59.5)“ 100(111, 121, 131, 141, 151) cm
Finished length: 21(21.75, 22.5, 23.25, 24, 24.75)” 53(55, 57, 59, 61, 63) cm
Sleeve to underarm: 19.75(19.75, 20, 20.5, 20.5, 20.5)“ 50(50, 51, 52, 52, 52) cm

Yarn used:
Sirdar Country Classic DK
Sade 865 Teal - 9(10, 11, 13, 14, 15) balls