What in the world should I build on Mordekaiser? (Mainly for Top)

I've been playing a lot of Mordekaiser in the past week or two, but I honestly still can't decide what's best for him. Should he be full AP, or somewhat tanky?

I normally build hex tech gunblade, but what other first one or two [core] items should be built on him or are equally effective? I'm going to assume the rest of his items are situational, but still, any tips on situational items?

I've looked up guides already, but I wanted to ask directly.