Rumble is a forgotten tanky ap carry. He is being played rarely but hes incredibly strong on top lane.
Pros:
Very Strong Initiating Ultimate
Very Strong Laning Phase
Very Strong Utility
Cons:
Hard to get used to the heat system(unlike any other resource system)
You have to get used to his ultimate
Susceptible to early ganks from strong gankers
Susceptible to crowd control effects

A great summoner spell. Helps you to escape ganks ,jump over walls, chase enemies that have a blink, get yourself in a better position.As previously said Rumble is susceptible to early ganks,flash should help you to escape them.

More killing power in laning phase,a very solid spell.

21/9/0 Is pretty much the only mastery build you wanna go for ,You can go 9/21/0 aswell if the enemy team got more CC or you wanna be more tanky.

Start with boots when you dont need extra armor or extra health pots ,boots can also benefit you from being able to harass better.
Once you get this item your laning strenght goes higher, Spell vamp coumpled with your Q is awesome.
Get these if you are againist a heavy AD .Go for those if you are againist champions like tryndamere.
Get these when the enemy team got heavy AP or loads of CC.
Great for easy lanes, the movement speed helps and the extra damage is noticeable. Be careful about getting these when the enemy team got really heavy CC or tones of AD!
This is pretty much the item you want to go for every game.It gives you a great utility. Double hitting enemies with your E will also make them move incredibly slow, you can also keep people in your ultimate longer cause of the slow.
Good item againist heavy AD teams, can keep you safe when the enemies want to focus you and your spells are on cooldown.
Good item againist AP damage teams, and as rumble you usually hit many people with the aura:D
If you feel you have to be a lot tankier you should definately build this. Especially with the HoG ,the extra health you gain is pretty usefull (watch out getting gp5 items when you lose your lane)
This should be your last item ,the 30% more AP passive is rediculous when combined with other AP items . Rushing this early will make you a squishy rumble and you really dont want this.