From how I understand it, slows stack. Therefore, if Skarner had Rylai's his q slow would make them even more slower, not to mention his skillshot would allow him to slow as well. Also, I'd need to test, but I imagine his ult might slow them as well, but I dunno if the effects would last longer than the duration of his ult. If they do, then that would pull someone out of position, suppress, and keep them from getting away after.

So basically, what do you think about having Rylai's on Skarner?

while slows stack, they stack in a way that reduces with each new slow. additionally, the aoe slow on rylai's is so little that, combined with q, it might not be noticeable
skarner also doesn't commonly build AP, forget why tho so go crazy if u want

That should probably read 'Skarner doesnt build much AP'. I usually see him running around with a RoA and an Abyssal to go with his Randuin's, Mercs, Shurylia's and Aegis.

Hmm... maybe I'm not playing Skarner right then... I always go Hybrid Bruiser build with him, focusing on AS/CDR and hybrid items as well as a little tanky.

For example, one build I like is first I'll go cloth and 5 pots, then philo stone -> mercs -> stinger -> wits -> shurelya's -> GA -> sheen -> trin -> nashor's

I've found this to be a very solid build as it gives him around 2.75k health, 168 armor, 150 MR, and plenty of damage, CDR, and AS to synergize with him abilities. Not to mention the GA greatly helps if you're getting focused, which, because of my ult, I find happening quite often.

Seems like a legit build. I love playing jungle Skarner and while this isn't the kind of build I normally use I might have to test it for myself.

I enjoy that build. The only thing about it is, since Skarner can spam his abilities constantly with this build, he can get pretty mana hungry. The philo stone helps early/mid game, but late game he can be pretty mana hungry in extended fights.