Some of the better class and items?

I don't know too much about LoL specifically (I mostly play Dota), but it isn't an RPG. You pick a guy that has strengths and weaknesses suited to your team composition and the enemy lineup, and your item build will follow from that.

List of champions here: http://leagueoflegends.wikia.com/wiki/List_of_champions, sort by type to get ranged dps

Read a guide for a specific champion to see what to build.