Hello everyone. The other day i was searching on mobafire creating item sets and applied them to the game that i was currently playing. I was playing 
kog'maw and the build said to build 
rage blade first but my friend said to build it second after 
essence reaver and 
berserkers grieves. That got me wondering about how to tell if an item is good to build on a champion? Thanks!
Your friend is wrong. I don't think you even build Reaver on Kog.
Nope, you don't. You want to rush Rageblade.
http://champion.gg/champion/KogMaw http://www.probuilds.net/champions/details/KogMaw
Use champion.gg and probuilds.net for references other than that trial and error
look at the item and figure out if it synergises with their kit. rageblade on kogmaw will pretty much instantly be at full stacks because of his attack rate, and hybridising his damage output by building it means the enemy team can't just get away with flat armour and have to build MR because otherwise you'll shred through them.
If you are winning trades more often than not, item build is usually good. If you find yourself losing trades constantly item build probably trash.
Are you winning with it?
Build experience comes with item knowledge and champ experience
Itll come in time
