Problem is right now that any buff they give him for the lane will buff him in the jungle as well. The only thing they could reasonably do is reduce base damages and increase AP ratios, but as long as he has that reduction to minions on his Q, he will never be that good as a full AP mage, because that (his Q before the nerf) was how he was able to lane safely. You can build him halfway between a mage and a fighter though. RoA into Deathcap and then Spirit Visage and IBG, picking up a Void Staff along the way. You can end up with 3300+ health with runes and you have adequate defenses and 500AP. (the reason I go SV and IBG is both for resistances and CDR, I always try to max CDR on Gragas, and take CDR/lvl glyphs for this reason). You can build Abyssal and Frozen Heart as well as this will give you similar stats (-HP) and if you have a Mage midlane, it might be better for the Auras. The disadvantage here is the lack of a spellblade item, which Gragas can make a lot of use of. IBG does physical damage so keep that in mind when building it. If you feel like you would rather have Lichbane, it's still very useful on Gragas, but it will be really hard to get the CDR in other items without sacrificing damage elsewhere.
I really don't like Athene's on Gragas even after the buff. It is about the same price as RoA, but it leaves you incredibly squishy and Gragas is in the opponents face a lot with his abilities (2 put you in point blank range of them). It used to be good when Gragas was a farming machine with his Q, but I just feel he can't be that kind of champion anymore with the reduction on his Q. He has to be closer to the action now to be effective. That is why I like RoA over Athene's.
That was more of a Mage build. You can also build him as a Toplane tank quite easily. RoA or Righteous Glory into SV or IBG/FH depending on lane matchup and team comp. Warmog's and Thornmail are good. Sunfire can help you with damage. If you are dominating, Haunting Guise into Liandry's + IBG makes you the peel master. Randuin's if you need health and armor. He does well with any tank item, so go for it.
I would recommend him in toplane over Mid though as he can get harassed by many Mages early on, but he does rather well against melee champs and tanks in top lane. Also, if you are getting shit on, you can easily start building tanky as you will most likely not be expected by your team to be the main damage dealer as would be the case if you were mid Gragas.
