Welcome to this Viktor build, in which I have created a build that gives alot of CDR that will allow you to slap your extremly potent combo out more frequently, yet still give you survivability and lots of AP.
For runes I attempt to strengthen my early and mid game and remain a threat in late game.
For marks I take standard magic penetration marks, for obvious reason. (You're a caster)
For seals I take armor, as you can be fairly vulernable early game.
For glyphs I take AP per lvl, with the agument advantage early game & the quints you wont need AP from glyphs all that much early game.
Alternativly you can also get magic resist glyphs if you feel that you need the extra surviveability.
For quint's I take flat AP, to strengthen my early game advantage.
For masteries I go for cooldown reduction, 9/0/19 to get the CDR from both trees.
With this item build you'll get a very short cooldown on your abilities (55% CDR) so you can slap out your combo more often, and also have the AP for your combo to be extremly potent.
Item number 1
I usually open with a Doran's ring for an early game advantage, although you can also open with boots, I do however recommend Doran's ring for the early game advantage it gives, you'll be able to poke fairly hard with your E without maxing it early, and your Q becomes devestating really fast.
Item number 2
When I can afford it I return to the shop to purchase Ionian boots, this is the first piece of the cdr puzzle.
Item number 3
Rod of ages is best to get as early as possible to benefit from its stats as fast as possible, so I get it before my augment. When I can afford it I return to shop to purchase catalyst or blasting wand, depending on how well you're doing. If you could really use some extra health and mana to stay in lane until you can get rod of ages, get catalyst, if you're dominating your lane (As Viktor tends to do) get blasting wand.
Item number 4
Your precious, precious augment that really defines Viktor. Some people complain that it's a waste of an item slot, but I beg to differ. You've three choices, power, gravity and death. For this build you'll go gravity, it gives 10% CDR (Which stacks up really nice with your boots % masteries, already you will have 35% CDR), also it gives some nice mana and mana regen, and your gravity field has 30% more range, which believe me, is really usefull.
Item number 5
Rylai's crystal scepter, a truely important item for Viktor. It gives much needed health, AP and a slow with your abilities. I usually return to shop when I can buy the giant's belt, then the blasting wand, or I just wait until I can buy the whole thing after giant's belt.
Item number 6
Morello's evil tome, this will give you a CDR of 55% combined with the other items, AP and mana regen, buy what you can of it when you can, but don't B just to buy small pieces of it.
Item number 7 (Actually 6)
Rabadon! Gives your abilities alot more power. Once you can afford blasting wand sell your Doran's ring and get that, then buy the damn thing asap.
Viktor's combo, as I've mentioned several times earlier is extremly potent.
With my build you'll be able to do lots of damage early game, so you're able to harass very well. Throw your Q at your enemy, and keep them in check & control the lane with E. Alot of people really underrestimates your E and thinks it wont reach them, but then it does! When you learn to aim this properly, the lane is basically yours to do as you please.
Anyway, when you want to throw off your whole combo, you do the following: Pop down a gravity field abit behind your enemy, to close an easy escape, pop your Q right after at your enemy, to get a shield rapidly followed by E, and finally your ulti and if you deem it necessary, an ignite. Your ulti + ignite when timed well is basically certain death.
Remember with your augment your gravity field reaches further, I frequently use it to attempt to trap my enemies @ towers & open up possibility to slap down lots of damage from my team and myself. Also remember that it can be used to save your teammates, just pop it down at them and your enemy will probably walk right in, as they will probably think of nothing but their greed.
As a closing note I'd like to add that you might always want to keep some mana for your gravity field, as if an enemy pops out of a bush it can completely ruin their gank.
As closing words I'd like to say that Viktor is truly an awesome champion once you learn him. He's a tad like twisted fate, in that you need to learn him to be able to play him well. Learn when and where to place your gravity field, how to poke and control your enemy with E and constantly harass with both Q & E (Not to a point you go OOM).
This build gives you amazing CDR, decent surviveability and loads of AP. Please test, and vote accordingly :) I'm open to critisism.