With the core items listed I racked up 13 kills and about 10 assists. Maybe not the most impressive feat, but it's still pretty good.
I believe a lot of people are trying to emphasize in his power area or health. Superman is beast enough that really you just need lobo's chain, some type of armor later, and stack attack to just make him beastly.
My rule of thumb with attack characters is that if an item I am buying costs 1000 or more, then I usually buy the Promethium mace so that way I have boosted stats in the meantime, then sell for the next item on the list.
Of course items on the list are situational and could be bought out of order, I mostly wanted to emphasize on the promethium mace aspect.

I will point out that for Gotham Divided I usually take soul taker sword before anything else, followed by deathstroke's claymore to make the most of the lifesteal.

His rotation will generally be
R > E > E > W > Q > Q
Or
E> E> W > Q > Q > R
I usually tend to keep R for that one champion who is very low health and about to get away, at which point I can kill him in one hit.

I personally believe he may be the best bruiser out there. So have fun!
Comments are welcome!