Build to burst people's faces off.
When you play AP Mid, the one thing you are expected to do is to chunk people's health. This is done through the way you build your champion. You need, NEED damage. Don't give me excuses: the jungler fed my mid, I need to build tanky/defensive against them. If you do this....how are you going to kill anyone? You're just putting yourself even more behind.
- Okay I get there are SOME exceptions, like going against a Leblanc mid, her damage is just broken early game. Even then, you can outplay her with ranged characters....like Xerath. Anyway, against Leblanc be a troll like Raina and start with 73 flat mr and ruby crystal as Ryze :D. Ryze's damage is broken either way g_g.
- Another exception getting the new item that builds into a Zhonyas, the armguard to go against AD Mids. Even so, before turning the item into a Zhonyas, you should get a Death cap first.
- Other exceptions are like...Ryze and Galio.... but the point is, you are expected to assassinate burst, and chunk people, if you can't do this, you're playing your champion and role wrong.
What NOT to do:
- I've seen too many people do this to ignore it.... Understand your champion....Ahri is an ASSASSIN. She is expected to be able to go in...kill a carry, and jump back out. Don't...don't rush a negatron cloak, and merc treads on top of that... you're making yourself even more useless because you wouldn't be doing any damage. You might argue "oh her q does true damage tho". Yea, but that's only on the way back on her Q, not all her skills are true damage.
- Do not EVER build health/tanky when you're dominating your lane. I had this enemy Zed against my Lux one game. His jungler camped mid, and I went 0/4 early in the game. The Ashe started complaining, but I told her not to worry because I'll be carry this game. You know why? I knew the enemy Zed would be useless to his team. What he did was rush a warmogs and other tanky items. Basically, his jungler camped for the wrong player. In the end, my Lux carried, one shotting their carries like a boss. (:
Which items?
What I usually start out with is a faerie charm and health+mana pots, and a ward if it's a jungler who can gank really well. But don't be fooled, I buy an early chalice, I just get it for mana regen. What I get one my first trip back is generally come dorans and tier one boots. If I got a kill and farm like a boss, I would get a straight up get a needlessly large rod. Then I would aim for death-cap the consider the grail, but if enemy team is building health and mr, I'd get void staff and Liandry's. My typical end-build is Death-cap + Sorc Boots + Void Staff + Liandry's + Grail + Either Morrellos or DFG, depending on the champ. Also, I generally don't get Zhonyas but if situation calls for it, it'd be another option for my 6th item. Only time i really get Rylais would be on a champion who really needs it...like Katarina and Ahri, but I'll be more specific in the guides for each champion.