What everyone has to realize is that the game is not cookie cutter.... This is showing my most common build
But you would normally only get as far as like raylai's and abysal and games over. The base build is raylai's and just counterbuild the rest of the game.
If you have another ap on your team or the other team is getting MR then get abyssal sceptor.
If the other team is heavy AD you will probably get focused so you need to build zhonya's. Just play proactive and counterbuild.
If your playing a morde they can be very tough to beat in 3v3 so build quicksilver sash to get his ult + an ignite off... It works so well and counters a mordes lifesteal so well.

So basically farm till you have your 3 spell combo and you can start harasing... you can get first blood easily with ur ult 1v1'ing most if you play smart and get creeps hitting them and not their creeps nuking you. And open team fights with ur ult and focus leveling your W and focus geting marks and stuns on there most dangerous character.