Heimerdinger Build Guide by FieldArmada

I do not fully disagree with your build, I just not agree. (that off course is the reason that you've decided to create a guide, and not leave it by mine ^^)
Allow me to name a few things I disagree with.

1. Getting your ultimate at level 10: this is pure suicide. It's not only the slow it gives, but also the passive CDR will help you escape a lot. You say yourself he is very squishy, and we all know he has no escape mechs. If you would level your ult, this gives you the ability to 1. use your grenade more often to blind/stun and 2. slow any incoming enemies as you're slow as dirt.

2. Getting some survivability very late in the build. I personally think that on a very squishy champion some survivability can make the difference. From my experience with Heimerdinger, his main problem is being bursted down in teamfights (especially in ranked stuff) by any burst that comes at him. For example, a Leblanc or Brand can easily kill him with only one combo.

3. Calling the Athene's Unholy Grail a "Bleh" choice. In my opinion, this item does not only solve your mana problems, it gives you some good cooldown reduction (this brings you at 39% with ultimate and masteries). End game you cannot rely on getting blue buff, because everyone will be roaming constantly, plus you will die from time to time. Also the extra magic resist helps out more than you might imagine :)

Furthermore I hope you will remove the name of your combo page or rename it, because this is obviously a copy of mine, or at least give me credit for it.

Besides these points, its a solid guide. If you could give me a good explanation for your choices or make these edits, +1 from me.