What are other good items on Warwick?

Should I change something on my build?

It depends on what role you think you really need to play as, as well as your current situation.

As a tank :

Get Golem and keep Ninja Tabi. Also consider the Wit's End, if your team really has not much AP damage. As a tank, avoid too much damage and prioritize armor. Thornmail can also help as well.

As an initiator :

Consider getting Banshee's Veil, still with the Golem and Ninja Tabi. As far as possible, build tank items like Warmogs/Randuin since you don't want to go ult an enemy then die in just a few seconds after.

As an AD Carry :

Again, consider the use of Wit's End or if you think your team has much AD, better go Black Cleaver. Better get other offensive tank items (e.g Hexdrinker, Mallet, etc.)

What do you suggest to build as 6th items?

As end game items, I suggest selling Golem for Zephyr. Again, consider your role. Having Guardian Angel can be useful, as well as Aegis of the Legion if enemy has good AP damage and you're fed early in the game.

I think I already answered the boots part. However, if you're losing in push (inhibitor destroyed), keep it with the Homeguard enchantment.

If you are wanting to go the Feral Flare build, only get 1 more damage item max. As a tanky jungler, you need to begin building defense sooner. A smart team will realize you are squishy and just focus you down making you worthless. Triple damage items can work in low ELO, but I still recommend going tankier earlier. This gives you an option between Wit's End or Botrk. Which should you pick?

1) Wit's End gives MR and steals MR from the enemy. Your ult, passive, and Q do magic damage and so this increases your damage output from all of these abilities. It gives bonus magic damage as well and increases attack speed for a cost of 2500g.

2) Blade of the Ruined King gives a slight amount of AD as well as % current health shred, attack speed, and a very useful active for 3200g.

Which do I choose? In the jungle, you typically have less gold to work with and as a melee you need to be able to withstand abuse from the enemies. The damage output from Wit's end and blade of the ruined king are very similar. Blade of the ruined king though loses usefullness the less hp the target has. The main reason I will go for Wit's end is that 700g pricetag difference. This lets you begin building tanky earlier. If you go 3 damage items and your enemies are smart, they will simply focus you at the start of every fight and you will be useless.

Now, that we have that out of the way, it leaves you 3 items for tankiness. Spirit Visage is a MUST for WW because he really benefits from the extra bonus lifesteal from his Q and passive as well as the bonus HP, CDR, and MR. (This can be your first or second Defensive item.)

Your real question should be what do you want for your Main Armor item. You really have 2 good choices. Randuin's Omen and Frozen Heart. Randuin's has a great active, HP, and enemies get slowed who attack you. Frozen heart has CDR, Huge armor, and an AS slowing aura. Either one can be useful. If you plan on building another armor item later, like Thornmail (their adc is tough for whatever reason) then I would definitely build Randuin's so that you can get that extra source of HP. If you are building a Banshee's later (Maybe the AP mages are blowing you and your team up) then go ahead and get that Frozen heart since it gives you that CDR, AS aura for the enemy team, and armor.

Final build:

Feral Flare, Boots, Wit's End, FH or Randuin's, Spirit Visage, Thornmail or Banshees

Ninja Tabi, Sorc Boots, Merc Treads, Swiftness, Alacrity(if you aren't getting FH) are all acceptable boots.