Rally is dead and i mourn for it. But enyone can now take surge instead. It works a little bit different so i will be updating this build accordingly.

I am going to play a midding Heimerdinger, that does not need rabadon's to do well and is hard to kill.

I prefer to get standard caster runes, namely:
Greater Mark of Magic Penetration for magic penetration
Greater seal of replenishment for mana regen
Greater Glyph of Scaling Ability Power and Greater Quintessence of Ability Power for additional ability power

Since your rockets have such insane range, you won't really need anything like Greater Glyph of Magic Resist or other defensive runes.

I prefer the new defensive masteries, since they fit nicely into my playstyle. Especially the ultimate defensive mastery is just pure awesome - Juggernaut gives you more HP and reduces crowd control effects on your person, allowing you to live longer and dish out more damage.

You can experiment with changing some less important masteries, such as replacing Mercenary by Expanded Mind . But the main idea is to get durable.

Start with a Chalice of Harmony. It is a perfect midding item for rocket heimer, simply because your rockets cost so much mana and your manapool sucks. Now how the hell is it good that my manapool sucks?! Chalice of Harmony gives you 1% more mana regeneration for each 1% mana you are missing, meaning if you have a small manapool and shoot rockets, you will get a decent mana regen bonus right away. Plus, chalice has +30 magic resistance, which is also pretty cool on mid.

After that, you have an optional step - philosopher's stone. Now if you are against some high-burst champion like le blanc / Malzahar, ignore this item and go straight for Boots and Giant's Belt. But should you be laning against, say, Karthus or cassiopea, it might give you just enough additional mana and health regen to make you unpokable. But since you already have mana regen from chalice and HP regen from your passive, this item is not necesary.

Get Giant's Belt and get it fast. Because after this, your enemies will have a really hard time killing you. Upgrade your Boots into mercury threads and turn the Giant's Belt into Rylai's Crystal Scepter in whichever order you want.

Continue with Zhonya's Hourglass. Now why not get Rabadon's Deathcap instead? You already have a slow and HP from rylais, why not get a heavy punch? It's simple. If you get your heavy punch, the enemy will focus you hard, and if they have someone like Nocturne, you might get killed before you even know it. Now i'm not saying it cannot be done with deathcap, but you need a really good team to back you up properly or you will die a lot, practically having big damage but being unable to use it. On the other hand, if you get Zhonya's Hourglass instead, you will either get focues and use it, or not get focused and be able to rocket / grenade / turret the enemy team to hell. And you will still have enough AP to make you punches hurt a lot.

So now i get Rabadon's Deathcap! Or not? If you love this item, get it, BUT:
1) Void Staff is much cheaper
2) Many champions in late will start stacking some magic resistance, which will make Void Staff a really huge damage increase, just as Rabadon's Deathcap. Remember, you will most likely not be hunting squishy champions with no mres, instead you will be in the middle of the fight, providing support for your team using slowing turrets, rockets and grenades for stun. And in the middle of the fight, you will be hitting mainly offtanks, which all have magic resistance by now, making Void Staff a really good choise. But if you love the silly hat, ignore the staff and buy it anyways - fashion is fashion.

Why mercury threads:
This build tryes to turn heimer into a damage-over-small-bursts champion. You have only your turret and 2 spells - once you fire your spells, the turret is your only dps. So you have 2 options on how to deal damage:
1) Stack enough AP to kill if one combo and kill them before they kill you
2) Survive long enough to fire second, or third combo and survive longer than they do - wear them off.

Since heimer has his turrets, i really favor the "survival" playstyle, which allows Heimer to run around his slowing turrets and throw rockets and a grenade every now and then. Mercury threads are ideal for running around - if you get slowed / stunned, it wears off sooner, plus you get mres to survive longer against magic damage.

Get the rockets. Then turrets. Take a point in grenade on level 2 or 4.

Place your single turret a bit away from the main minion path, a little bit to the brush into the river. That way minions will not usually kill your turret and you can fall back to it should gank arrive.

Ignite + Rally.
Since heimer is positional, rally is quite cool with him. But i expect it to be replaced with surge after the patch.

Also, if you don't like it whatsoever, get Flash. I wouldn't recommend Teleport, simply because of heimer's awesome lane staying power.

Here it is, guys! Heimy with rally.. and without the silly deathcap, that wouldnt fit on his spagetti hair anyway. Leave your interesting or creative comments in the comment section below, or on.. well, just type them below. See ya.