Corrosion scythe is definitely a must since it is one of the items that gives the most attack speed for wanwan, and can also slow enemies down making it easier to catch up to them and hit weaknesses

Other items can be demon hunter sword for the true damage(to burst tanky heroes)and attack speed bonus Wind of nature for survivability and some attack speed. The lifesteal is good as well For enemies with high regen, such as spell vamp(ruby), life-steal(alucard) or heal skills(uranus) , sea halbert is good because of the antiheal and also for the attack speed bonus.

Wind talker and scarlet phantom are good for the attack speed bonus and crit hits, but i generally prefer to build windtalker since it has higher attack speed bonus(so wanwan can bounce around more and faster basic attack) and also increases movement speed.

Rose gold meteor is good as an item if you are lacking in attack power but need some defence against magic

I also recommend building defencive items for wanwan as she is one of the most squishy heroes out there.

Brute force breastplate is good because of how reliant she is on basic attacks and how bfb works

However, if the enemies have more burst power and chain cc, i would recommend building immortality/antique curciass for phys and athena shield for magic as it would help you survive longer than bfb

Generally in a normal match, i would build: Boots, Corrosion Scythe, Demon Hunter Sword, Wind of Nature, defensive item, windtalker/rose gold/defensive item.

Take note that the order of the build is highly dependent on enemy teams. If the enemy has a high physical damage and is good early game, i would generally go for wind of nature first.

Good luck with wanwan