Hello everyone and welcome to my first build guide. I am Boolono. This build won't be flashy with lots of pictures or what not but you will see the proof is in the play.
Now I am making this guide because I feel Rumble is a very strong champ who is also very, very underplayed and when he is played more often then not is built incorrectly and gives the champ a bad reputation leading to him getting played even less and not bought at all. I am here to lay that to rest with my guide for the Mechanize Menace because he sure is one.
This build turns Rumble into a super hard hitting caster carry who can destroy turrets and teams alike. With this build you can juggernaut your way into 5v1's and come out with three kills and still be alive to take out any one who tries to fight you again.

With this build you can take Rumble anywhere: mid, top, bot as an anti-carry, even support. His legendary harass and sustain let him do what he wants.

Pros:
No one plays him so no one knows his move set or how much damage he does
Great escape and chase, can sprint across map
large amount of slowing potential
Ult has insane range and massive damage against teams or single targets
Fun to play
If fed most teams would rather run away from you than fight
Can fill practically every role on the team if needed
Cons:
Early game before spell vamp not super durable
When fed people avoid you so you stop getting a ton of kills
If gets super-focused escaping takes a lot of skill to do but very possible (spam dat shield)

The one flaw Rumble truly has is his early game power without flat AP. If you don't have flat ap runes and masteries your damage can be ignored, but if you have flat AP at level one your double harpoons can take out a quarter to half of your opponents health.
The flat armor seals are for that early game survivability mostly, though they are a help all game, since every single champ deals ad damage.
The marks are for increasing his damage all game.

Rumble is built to be a slightly off tanky caster carry. His masteries are set up to deal the most ability power damage possible while still giving him some survivability in his armor and magic resist. You will build more of both later in your build but this helps you early before you have Zhonia's and Lichbane built.

This build is not set in stone but you will never go wrong with it and it counters all situations practically, the only thing you might want to change is the order of purchasing the last four items in the build. This I will always say on first recall always try to get revolver, your flamespitter, rumble's q, does so much damage to the area in front of him that you will be healing constantly and the hits from harpoon will heal for decent chunks of health. Once you have revolver you will instantly win lane practically everytime and if the enemy jungler decides to gank you, you can kill him and the person you are laning against. Spell vamp is the key to Rumble.
Anytime you recall and can't buy a big item in your build elixer of brilliance is an excellent buy, the AP and the CDR given by it will completely throw off your lane opponent with your even more insane ability to blitz them with your entire arsenal of moves and will help keep your ult ready.
There is one item that synergizes with Rumble like no other, Rylai's. In a word permaslow. Every single one of your damage move will slow especially flamespitter, no one can out run you. And when you hit them with the stacking slow from Electro harpoons they will be at such a crawl you will run donuts around them. And it will boost the already insane slow on your ult vastly increasing its effectiveness.
Lichbane synergizes so strongly with you constantly procking it with every single one of your moves allowing you to deal 1000 plus damage in a single hit without overheat on, with over heat you will deal, 1500 on your first hit, this applies to turrets, champs, anything dumb enough or not fast enough to get away.

At level one the move that gives the most power is Electro harpoon and you get two shots of it and a slow.
Flamespitter is your main damage so max this first. Your shield is your chase move, escape, survival, dive move, its everything. With it and one or two hits of Electro harpoon you will leave anyone in the dust, even Rammus will be choking on the cloud as you gas them. at level 5 the shield comes up every 5 seconds and gives a speed boost, more if you are in danger zone.
You max shield second taking the utility in Harpoon last.

His passive is absolutely beautiful. Each of his moves except ult gives you 20 heat, at or over 50 heat all of your moves are 33% stronger, so try to stay directly at 50 as much as possible.
This allows you to instantly using all your moves, saving flamespitter for last which continues while you are silenced, snared, stunned, suppressed hard cc does not stop it, so you go into Overheat with the flames going in front of you.

Overheat, so severely misunderstood even by Riot in their tips for going against Rumble. They say Overheat is the time to engage Rumble, they forget to mention this is when his melee attacks late game can do 400 to 500 damage per swing. So not a good idea if you are within the range where he can punch you. The only disadvantage Overheat gives is that you are silenced for its duration but it effectively works as a steroid for Rumble so it is more help than hurt. Though if you don't manage it well it can very easily kill you if executing a move could save you. It is a situational move for dueling or fighting in the middle of the enemy team. It is not good for chasing or escaping at all.

His ult does insane damage all game and has absolutely ridiculous range. It does a large initial hit and then slows dealing triple digit damage every second to those caught in it and for a fraction of the time after they leave the ults area of effect. Your ult can be used on solo targets to assassinate them from long range, to slow them so you can catch up or to ult an entire team that has formed itself into a line to fight you. Fight in your ult as much as possible its damage is so high people will melt away from you.

Your job is to kill everyone in front of you and push waves like there is no tomorrow. You can almost out damage anyone who comes against you and you can fight multiple people at once. Your main sources of damage flamespitter and ult hit several targets at once so go into fights ready to wreck. If you are in trouble activate Zhonia's and prepare to sprint away from the fight. Always sprint away at 50% heat because an additional 33% speed boost is very nice.

A very strong carry champ that is severely underplayed. You lane against anyone who is mana dependent and it is practically an assured victory with your constant harass. Abuse your ability to be able to always use your moves and remember, Juggernaut Rumble knocks them down like pins so they had better get out of your way, with this build I average 15+ kills and around 2 deaths in ranked matches and receive friend request all the time for my play. You will enjoy Rumble.