So i've found that i use an unorthodox rumble build. i find it to work as an effective build in most situations.

I use magic pen marks, attack speed seals, 3 magic pen and 6 attack speed gliphs and magic pen and 1 movement speed quints.

my masteries are 9/21/0

9 offence for CDR and magic pen

21 defense for rumbles squishyness

i start with dorians shield for lane staying power, followed by boots of speed or sorcers shoes for the added speed for chasing enemies and magic penitration for boosting all of you abilities. if their team has a lot of CC you should go for murcury treads for the magic resistance and reduced CC. next i pick up a haunting guise, the 20 magic pen and 200 health help rumble with his squish and increase his damage output. i like to play upclose and personal with rumble so next i pick up a malady. the added magic pen and attack speed works wonders when he reached 100 heat. at this point the are a few ways you can go. if the other team isnt smart enough to pick up some magic res by now you dont need a void staff. you can go for a rahabodons deathcap at this point or if you are taking a lot of magic dammage i recomend a force of nature. if you are recieving a lot of streight dammage from melee or non magic i recomend a thornmail. the returned magic dammage is just like your passive and all the magic pen you have by now is doing a Lot of dammage. an other option is getting a guardian angel. in the late game ive had guinsoo's rageblade work very well for me, the attack speed and AP work twards all your strengths and keep the cooldown up on your malady. a hextec gunblade or will of anchents can only help at this point and will help your staying power.

i max Q first followed by W with a point in E at eather 2 if u need to assist a slower player in ganking early game or 3 if u you are getting pushed early on. always put a point in your ult when it comes up.

for almost all champs i use ignight and flash. flash for chasing and evading. ignight for finishing off enemy champs that think they can escape behind the turret.

heal would be benifical if you are new to rumble or find yourself overextending often.
you can use ghost for chasing and evading but i find flash to be more benifical if you are proficent with its use.

i find that laneing with a champ that has stun/taunt/fear or any other CC that will hold the enemy in your ult for a second longer will take that much more life off the emeny. i often play with an Eve. her stun and rumbles range on his ult are an epic combo. also if someone stuns and you reach 100 heat from using Q the extra attack speed and magic pen from malady/guinsoo's rageblade will really show their colors.

i love the description of rumble as a bully. i often solo mid and can hold off champs like caitlin or ashe with ease. even champs like karthus and casiopia tremble in fear at the thought of rumble. keeping eneny malee champs off your creeps is very easy with your Flamespitter. if you keep your heat above 50 you can cut through crouds of creeps with ease. if you want to last hit avoid using your flamespitter untill champs like brand use their piller of flame or cho'gaths' rupture.