Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
This is the first build I post and honestly I do not know how it will work "very" late game because I haven't reached it yet with this build. The games usually end at 45 minutes +- sometimes sooner. I hope you like it and if you don't please tell me why in the comments because I'll be using this build and if there's anything to improve that would be awesome :D.
I personally like my items. They're not great for survivability but they've won me a lot of games already.
The gunblade speaks for itself : 25% spell vamp + 20% life steal => Rumble uses both melee and magic.
I've put a lot of thought in the Rod of ages and if there's a possibility to change it , I find a lot of its bonusses are wasted in the extra mana but I think it's worth it for the HP and AP.
The Mercury treads are in my opinion really needed because Rumble gets up close to his enemies and is vulnerable to CC
The crystal scepter is one of the items I would never take away from Rumble. It gives a huge HP boost and some AP. The real beauty lies in its passive , the slow + flamethrower makes it a real pusher and killer.
The hourglass is one of the items I took for the armor + the AP. 100 AP is really nice and the active isn't bad either if you use it right(ahse, ezreal , lux , and more ultis can be blocked)
Rabadons is just for the AP it gives.
You might want to alter this build and change rod of ages / hourglass for void staff or abyssal scepter depending on how magic resist heavy the enemy team is going.
I chose armor/magic resist for runes to improve the survivability. I've seen a lot of builds do this and also believe that it is correct. => make up for lack of defensive items
Magic penetration runes are just awesome , they can be used with almost any hero and will almost help you dish out more damage.
The quints I chose are just in general truely awesome. I cannot see the use of 3x quint of fortitude. Those will only help early game but you will benefit from speed all game long.
(I don't have them all yet because I cannot afford them yet.Used to play Veigar , still have mana regen xD)
I didn't really know what to do with the masteries so I just did the thing above. I wanted to go for utility for CD reduction and +3% walk speed but that would waste too much mastery points for those masteries. I got survivability because I don't get any tank-items which rumble kinda needs.
I hope you like this build and I hope I gave enough explanation for my items , runes , masteries. If you see something which could be better don't hesitate to post. I hope I forgot nothing , I'm forgetfull :P