Not Updated For Current Season
The only reason why I didn't have all 6 items in the item build is because it depends on what your enemy champions are.But the items I listed above are items you should always get as they are very helpful.
If you are fighting tanks:
Boots of Mobilty
Elixer of Agility
If you are fighting DPS:
If you are fighting Nuke/CC:
Early Game 1-6:
So at the start of the game you want 1 point into raise morale.Wait at your Nexus until the creeps spawn and use raise moral on the first creep.Now go to your lane and when you get to the enemy creep the CD should be done and use raise morale again.You want to only use raise morale to deny your oppenents EXP.NEVER use your mana for parrley at early game as it won't do much damage and you are better off with denying there EXP.
Mid Game 6-12:
Now then you should have Manamune and mana should be no problem.Now keep farming until you can get your Infinity Edge since it is your main damage item.Use your ult to help your partners get kills or save them from dieing.Keep denying the EXP as well.You should be around 2-4 levels of everyone on your enemy team if you deny them well.
Late Game 12-18:
Now that you got your damage items you should be able to 1-2 shot the low HP champions.Everytime in a teamfight cast your ult and look for the DPS/MAGE and Parrley them.They should be down to atleast 25% HP and they will have to fall back,but if not finish them off.Your main job is to Parrley all the low HP champions and take them out.
I hope my guide helped you guys and I wish you all luck :D