Thank you for the comment. I'll try to answer your questions in order the best I can.

1. I like to get attack speed runes because you can never attack too fast. The small amount of Armor Penetration that you do get will be nothing to the amount of attack speed you can get. It is personal preference really. Everything about this build is.

2. With this build, you get your boots first and then you get two zeals, thus meaning your run really fast. I have never needed a level in Undertow in order to chase or get kills early game. If you feel that you are having a hard time chasing without Undertow then I would suggest getting it at Level 5.

3. Although this build seems expensive, I usually finish the first Phantom Dancer in every game that lasts around 35 - 40 minutes. You get so many kills from mid game to late game, and sometimes even early game. This isn't always true, especially on those days where I just suck as Olaf, but for the most part that is what generally happens.

If you want to test anything that you feel might be better please let me know the results and I will try it myself. I would like to better my build as much as I can and thanks again for the comment. :D.

Good build. I like the rune choices maybe get armp for marks or quints since you have a bunch of attack speed from your build. Also I think you should get one level of undertow before level 6 just for situational purposes. I think this build relies on the game being long though as all your main items are pretty far in especially frozen mallet, you might want to purchase a phage and 1 level of undertow before 6 and you're good! :)