Runes :
Magic Pen reds , Armor yellows, CDR blues vs ad or tanks , MR blues vs ap and Ap quints
Masteries :
Sorcery, Double edge sword vs low damage opponents, Feast vs High damage, Natural talent vs low damage opponents, Vampirism vs high damage, oppressor , piercing thoughts and DeathFire Touch. Savagery , assassin , merciless and dangerous game.
Builds :
Boots 4 is what I usually start as Rumble, although it can be cloth 4. If I see my lane going poorly , I rush Hourglass , since I would have to buy it at some point, and it helps stay alive, at least for a bit longer. If I am doing well, Liandry's it the best option. Void staff is a must have, as is Rabadons, and Rylais helps amount your damage. If against a Ap , rushing Abyssal, if ahead or behind is viable, since it gives you resistance + very good damage (the removal of MR is underrated, especially as Rumble ) . I saw you try to buy, Gunblade I believe, in game 1, and let me tell you, it's not good. He would much rather the magic pen then a Gunblade, even if he autos a lot.
Lanes to avoid:
Unfortunately, most lanes are poor match ups currently. Bruisers were already a counter to Rumble, and they got buffed in the preseason, so Rumble is kinda in a bad spot right now. Fiora, GP, Irelia, Mundo ,Garen , Darius, Jax, Wukong, Rengar, Olaf, Garen , Tryndamere, Ekko, Jarven, Swain , Trundle and Riven should all be avoided.
Lanes to pick into:
Rumble is good against targets that have no CC (Fiora and GP are the exceptions) since that means that the lane will have straight out duels, and Rumble outputs massive damage. Illaioi , Teemo, Mord and Poppy are good lanes for Rumble. He does fairly well against most tanks (Just , avoid Mundo, please) since he can outdamage them + he builds Liandry's , that counters their health stacking. And a Final note is that he fairs well against most Ap champions, since he can afford to rush Abyssal, and proceed to take over. Lissandra is a great lane opponent for Rumble, despite her CC overload.
Suggestions :
Your passive does not trigger against towers (The more damage on auto while silenced), so spamming spells will not help you take down the turret faster, and can leave you exposed to jungle pressure.
Your passive does not boost your ultimate's damage, I've seen so many Rumbles use their spells , almost overheat and then ulti, thinking that it will do more damage, but it's basic spells only.
Speaking of your ulti, I recommend that you remove smart cast if you have it on. Landing a good ulti is already hard, but using smart cast makes it even harder.
A neat trick that evolves your ulti and a Hourglass. As you may know, Rumble does not have any escapes, so while dueling or being ganked, lay your ultimate on you and activate the hourglass. If they are melee, they probably will take a huge chunk of damage, that will hopefully prevent them from reengaging.