Predecessor Builds > Feng Mao > Offlane Domination - Feng Mao
You can't tell me Feng Mao isn't in the meta unless you have tried this build!
Feng Mao really struggles against Grux in lane. He will get bullied out regardless of build. If you know the enemy offlane is Grux, avoid this hero.
Personally I prefer Nex for the late game combos when cooldowns are short. Ortus is also a perfectly reasonable choice.
Always start Infernum for the early game tick damage and mana which is definitely helpful for Feng Mao. Malady is a must! If you are farming well, Malady should start to be built around the Level 6 mark, which is perfect synergy with ultimate unlock for the easy kill confirms and Malady stacks. I don't see a lot of Feng Mao builds include Earthshaker, but this is also a must have item. Helps build around Feng Mao's brilliant ability damage and provides extra sustain in lane and atk. speed which feels really good on this champion. Nightfall again is great for the mid game sustain in longer team fights with the extra lifesteal. Boosts lifesteals for ability damage, so synergises well with Earthshaker. After this item there is a few options.
I personally will almost always go Penumbra for the fantastic 20 ability haste and extra bit of health. The pen is obviously super important throughout for ultimate damage. Last item I have put as Augmentation, but again this is flexible. Augmentation builds more around that ability damage.
Dependant on the match, last two items could change to enable a bit more of a bruiser style build. For example, Draconum or Dread. If your team has a strong late game lead, so more damage focused items could also be Deathstalker for the atk speed boosts or Envy for the guaranteed crits and boosted combos.