Good rumble guide. I run rumble almost the same way. Rumble really needs magic pen because his spells are all DoTs which do a teeny bit of damage each time they hit. All it takes is a little magic resist to cut Rumble's damage down to nothing. Also all it takes is a little bit of Magic Pen to cause squishies go negative magic pen on you and take increased damage.

i understand why you get electro harpoon first BUT you cant harass **** at this level. And you shouldnt get rylais crystal scepter first. that should be gotten about last. Your tank items arent tanky enough. you need flat tank items. like FoN or Sunfire. AP isnt much of a deal on him seeming his base damage rocks already and AP wont effect his Q a whole lot. Just grab a mejai's first then go flat tank items after that. you will have both good AP and tank items.

The reason it says you don't have Sorc Shoes is that you have 6 final items in the build after it. The guide just assumes you keep the latest 6 items, I think.

I'd recommend testing out flat HP instead of scaling if you want to help your early game. I do flat armor seals myself, but HP is pretty good too for serving that purpose.

A minor point, you say that Haunting Guise won't help while overheating while gunblade does. The extra damage is magic damage, so magic pen actually does make a difference. I agree gunblade is probably better at that point, just clarifying that point.

Overall, good guide. +1.