Im posting this guide for 2 reasons.
1)New players may have hardships on choosing items.
2)When i try some original build in a low team and we get pawned because of their low skill + innability to understand that, i get flamed/spammed with random oppinions and i hate it.

How to choose what items to make? Item Efficiency
When you pay X for an item you gain Y power/chance to win. The higher the Y/X is, the best for you and your team. Power/chance to win is related with your ability before and after buying the item to be Useful (Stay in the map, Deal/Withstand good amounts of punishment, Annoy/Push)

***Being Useful doesn't mean farming all the easy creeps in the map but actually being a threat to the opponent team.***

Based on this logic i categorize items in 3 groups. Efficient, Deceiving and Bad.

An efficient item has good Y/X. That means that the specific character gets from this item what he paid for or even more due to some Synergy.

Example: Kayle + Rageblade.
i)The item synergizes with her passive.
ii)Righteous Fury needs IAS to be more effective.
iii)With good skill rotation she can maintain the AP/IAS buff.
As far as i can tell this is an Efficient item for Kayle.

Example: Kaiser + Mana Sapphire.
LoL wut? This is the perfect example for a Bad item choice. No need to Clarify it. Does that mean that Mana Sapphire is worthless? No. It just wont synergize with any of Morde's ingame roles.

There are item/champion combinations that have the exact same effect as the above but at a lower scale, so that it is hard to spot or understand it.

Example: Ezrael + Manamune
First thought could be: "Why not?" its a rather cheap item, it helps you spam/farm and increases your Auto attack + (Q) Damage output. Well... WRONG!
i)Ezraels Q Has only 50 Mana. If you Play him AD you use auto attack. (The other 3 spells are situational on the AD build)
ii)Q animation stops your auto attack. (His other spells also) That cuts from your autoatack damage output.
iii)Tear of the Goddess man pool will build up rather slow.

Manamune is a deceiving item for 80% of the cast out there. It is efficient on 3-5 Champs at the most and wont turn the tide ever. Be very careful.

Example: Corki + Manamune
i)Corki has Expensive skills so he needs the 1000 bonus mana.
ii)His ult will help him fill the Tear of the Goddess, (Unlike Ez,Sivir)
iii)The Bonus Damage affects his Ulti + His machine Gun + His 600 range Auto attack + His passive pure Damage (Machinegun can be used simultaneously with his Auto attack as well)

Manamune Costs all this gold because of the Y/X it offers to champs like Corki. Its Y/X for champs like Ez/Sivir is much lower.

Just because its Y/X is not 0 ,like Mana Sapphire for Morde, doesn't mean it is an efficient item for Ez/Sivir.
If you find your self losing a lot consider your build efficiency among other factors.

That's the link to my Kayle Guide:
http://eu.leagueoflegends.com/board/...ad.php?t=85040
And my Pantheon Guide:
http://eu.leagueoflegends.com/board/...ad.php?t=89238

a lot of txt, nothing original.
spare the time- no need to read

I see your point.

TL;DR: Don't buy mana for mordekaiser (Just kidding sir please don't kill me)

Vasifan, ye olde scumbag.

I see what you mean, but I'm afraid it's not that simple, you see, the items you choose improve your champion in many ways, from which his skills will benefit. HOWEVER one more thing that benefits from the items you buy is your own playstyle. For example, when I started playing with Shen I looked up the guides and most of them took either Ruby Crystal (synergy with his passive, more HP) or Doran's Shield (HP, HP regen, armor, very useful if getting harassed), However, due to my playstyle, which incorporates last hitting mob with Ki Strike and Vorpal Blade, and after I get Vorpal on lvl 3 I pretty much harass one opponent non-stop with it and just last hit with auto-attacks.

This play-style often got me killed, not because I didn't have enough HP, but because I didn't get enough HP regen to recover from harassment during laning phase. After weeks of experimentation I found out that the best starting item for my play-style was Regrowth Pendant. Should I ever get harassed, I can synergize it's insane regen with Vorpal's life tapping to quickly be ready to take more punishment while my opponents run out of mana. I never have to leave a lane like this, and later I can upgrade it to Warmogs, which gives me delicious Ki strikes.

Always when you're buying items, consider how do they affect your skills AND how they can be exploited with your playstyle. I remember seeing Tank Annie wreak havoc in one game, and the only synergy it had was with Molten Shield, however the player was able to use them with his unique playstyle.

I never said its simple... Im just trying to put it up simple.

Te main goal is to be threatening throughout the game.

From my point of view your Shen example enhances my theory.

Dorans Shield may be more efficient in general (Greater Y/X) and ruby Crystal may be a Great burst counter but when you mix up Shen in there...

Shen has Great resistance to burst damage due to feint, HP pool and dash. During laning any burst attempt against him results to a simple poke (Since portion of the damage is absorbed from feint)
He will rarely find himself "surrounded" due to his high mobility (Dash) as well.
(Also you dont need to buff ki strike Early since you have hard time landing it, being melee).

The only way to kill him is to poke again and again until he is vulnerable to a burst.

Regrowth pedant counters this more effectively so it is more efficient.

I agree thet Playstyle has a major role to item choices. My intention is to make clear that some items that seem "Good" are not.

Tear is a good item on sivir because WHEN you upgrade it to a manamune it builds mana from normal attacks as well as skills.

Sivir also heavily needs the bank.