1. Cloth armor + potions
2. Upgrade to madreds razors
3. Get boots
6. Finish madreds bloodrazors
7. Finish boots (according to the other team)
8. Now this is the part that gets confusing. (A is the usually the best and F being the worst)
A. Guardians Angels are probably the best for most situations. Warwick is usually one of the first to get killed in a teamfight and this will discourage them from targeting you. + the bonuses are nice.
B. Wits end. This item will add the most damage to your ultimate, other than blood razors.
C. Black Cleaver. Also great, not as much damage as Wits end, but usually your second choice if the other team has little mana users.
D. Last whisper. Good for taking down tanks such as rammus that are armor stacking and such.
E. Sword of the Divine. If you see a jax or a someone stacking dodge.
F. Banshees veil. This item is probably best if your getting disabled, but not targeted. For example. Annie has swirly and uses her ultimate on your buddy jax which just so happens to be right next to you. You get stunned and killed by her aoe, even though she wasn't aiming on killing you.
9. (optional, something you didn't get from the list above) If you didn't get GA before get it NOW!
10. Finish the game!