:
750 AP with blue buff, granting over 1000 HP; barely less without blue.
bonus HP: ~1500 (~3500 total)
AP: ~750 with blue, 675 without
bonus MR 60
bonus armor: 50
CDR runes required
:
bonus HP: ~2000 (~4000 total)
AP: ~460 with blue, 400 without
bonus MR 55
bonus armor: 50
bonus healing: 20%
CDR runes optional
Abilities (without blue)
AP
Q damage/heal: 506 / 276
CR Q damage/heal: 1012 / 476+ 560 at 50% HP.
E: 414-1065
R damage/heal: 823 / 823-2468
Bruiser
Q damage/heal: 355 / 216
CR Q damage/heal: 710 / 416+ 504 at 50% HP.
E: 330-820
R damage/heal: 630 / 756-2268
As you can see, the only thing bruiser build holds over full AP is rocket belt, not needing 10-20% CDR from a runepage (depending on boots), and ~500 HP. The HP is essentially invalidated by the advantages of the AP outside of pure burst situations against you, which don't happen unless you messed up really badly.
AP steamrolls bruiser during mid-late game.