Do you guys still think he's viable as AP? Is his skill set and AP scaling on par with other secondary mages? What do you guys think? Gragas is my main, and I'm not always inclined to play him as a Tank. I'd like to play him as AP, but everyone gets mad at me when I do so, even though I usually come first or second in damage.
He is still very strong ap yes
Not really. Malphite AP is honestly better in almost every way Gragas has everything a tank wants right now passive % hp sustain Q for aoe damage and slow W for % health magic damage and damage reduction E for CC and mobility R for aoe displacement
A few months ago, you would have gotten yelled at if you were building him as a tank. He's better as a tank right now, but with the change to Athene's, he can actually go AP again. The damage reduction on his Q to minions is really what's holding him back from being an extremely viable AP champ. His AP scaling isn't terrible and he has CC and mobility with a lot of magic damage. The reason AP Grag used to work so well is that he could stay back and farm all day. If you got even remotely close to him, he could slow you, stun you, ult you away, or simply E away from you. And then he would go back to farming. Now AP Gragas can't just Q to clear an entire minion wave, so he has to walk into harms way to CS. AP Gragas can work, but you have to be so much more careful.
Build-wise: you have options.
You will start either 
or 
as a first item. RoA will be a more tanky version of an AP build, but you can still do decent damage.
In the RoA build, you will get 
the reason you go Lucidity is that CDR is very important on Gragas's damage output as well as his survival. At near max CDR, Gragas's W is on less than a 2.5 second CD which means he can ALWAYS take reduced damage (this is also why tank Gragas works well). I also take CDR/level Glyphs when playing AP Gragas to help get close to the cap. Other options are to go 
but grab CDR in another item such as 
or 
but that will end up doing less for your damage as you will be sacrificing a slot for the CDR. The rest of your build will go into increasing your burst damage in your full combo, so grab 
and 
to finish out your build.
The Athene's build is all about maximizing damage from your AOE abilities. While using your other abilities more cautiously as you are much squishier. You will still want to get a Deathcap as soon as possible to make it easier to clear waves but you will most likely not build a Lichbane. The full build will look like a standard midlane mage build. and the last item is a choice to build a defensive item or to get more damage with any of these items 
as they all work fairly well with your kit in different situations. Rylai's helps you kite better. Liandry's is okay in siege scenarios and extra pen is always appreciated. And Lichbane adds more burst.
The new item 
might be a good second item as it gives you the extra damage you need to clear waves and can boost your harass on a lane opponent. I would recommend trying it out, but only as a second or third item, as it's extra boost in damage is best in the early game. Consider building it as a second item instead of Deathcap, and then save Deathcap til later. I think it has good synergy with his kit as he can cast his Q, let the barrel charge while walking around and using your W to charge your Luden's and then pop it once the stacks hit 100 to get the extra burst in damage. His E gives him a Dash and a cast to help charge his Luden's. Try it out. Peace.
Ap gragas works wonders with a lichbane and full cdr. Since his w deals % damage with a low cd, he can consistently body slam a person, w em and use q's slow as retreat. I play gragas mainly on dominion, but he can beat the crap outta tanks and usually wombo combo the squishies down with little effort. If you're the only frontliner though, i'd suggest going tank.
He is still decent as an AP Mage type of champ, but is considered pretty squihsy if you're planning to go glass cannon. Getting a Banshee or any other tanky items is good for you.
And if you're wondering, no, DONT BUILD AD GRAGAS. Js :p
Barrel bombs of death. You don't need boots because your enemies die in one barrel pop.
