Bottom bracket, Groupset (crankset, front & rear mechs, gear/brake levers, brakes, gear and brake cables, chain), headset, seatpost, saddle, wheels, tyres, inner tubes (then the extras like lights, bottle cages, mudguards, saddlebag etc), plus the various specialist tools
You may well find it was cheaper to buy the whole bike in
Halfords Boardman sale (15% off ends today + a further 10% discount for British Cycling members)
Happy building however