So fiddle sticks has always been known as a great champion 1v1. This is because if he is using his drain on one opponent who is also attacking him. he loses little or may even gain hp while the opposing champion dies. This build is going to make it impossible for all of those pesky twitches and evelynn's to be effective. Because really the only way to beat fiddlesticks is run from his drain, stun, or silence him.

Start with a mana crystal to be able to lane longer. also buy one mana pot. the reason for mana potions instead of hp potions is so that you can use your drain on minions to keep your hp levels high. The first time you recall you should be able to afford Catalyst The Protector Which makes so you can stay in lane longer because of the extra HP and MP you get on leveling.
After catalyst you want to get your boots then complete the build for Rod of Ages. Rod of ages early game is smart because it makes so you get its passive stats earlier too. After Rod of ages your going to want to buy Archangels staff. This will be much more effective because of the bonus mana from rod of ages and it will leave you with way more mana. After that buy rabadons deathcap to maximize AP. By the next time you recall you should have won by now but if you havent it is smart to get Rylai's crystal sceptar this will give you ap hp and makes all of your spells slow.

So this build ends u up with a lot AP, HP, and Mp. (mostly ap) By far the best build ever for fiddle sticks. Basically all fights go the same way. You engage with another player and then u fear them and use your drain. with this build you will be near indestructable because of a combonation between base Hp and how much is returned by your drain. When you have Crowstorm up you should never be afraid to jump in for a 1v1 (even a 2v1 if the game is going good). This is how that fight would look: you stand in a bush or on the other side of a wall so the opponents cannot see you channel. Then after the channel is up you fear the enemy champion so he is trapped in area of effect and finish them off using drain. There is no room for a slow reaction between your ultimate, fear, and drain. use each spell cast within a second of the other.