The Item Build is mostly very game dependent. It's important to build against your lane opponent and the whole enemy team. So if you play against a really heavy Ad toplaner you rush Iceborn Gauntlet the item gives you mana+the passive+armor overall it is a really nice item aginst heavy Ad's. It lets you push towers way faster aswell. But if you play vs a tanky toplaner you should buy some damage because Nidalee has a high standart damage but she has not that much standart damage like a Malphite or tank Renekton. In that case you should buy a Phage>Trinity Force or a Bilgewater Cutlass>Blade of the Ruined King to fight your lane opponent. After one Ad item you should build some resist like a Randuins Omen or a Spirit Visage (depends on if you play against Ad or Ap). Later in the game you should build some of the items which are listed in the top.

In the early levels you can use Nidalee's auto attacks in her human form to poke the enemy toplaner and zone him with that poke. While you are poking him you can freeze the lane pretty good and just last hit the creeps that the enemy toplaner loose some creeps. With the new passive after the rework you have a pretty good early kill potential When you hit your Q in human form you can switch into cougar form and jump onto him to deal him a lot of damage which is pretty good against toplaner who are not that tanky like a Riven, Rengar or a Tryndamere.

In the midgame you should still farm on your lane and if your lamer roams follow with your teleport when it is up when it is not up you can splitpush pretty good with Nidalee's "E" in human form because of the massive attackspeed buff. Nidalee is still pretty good in the mid game so you can figh your lane opponent still good (just if you have a item advantage or level advantage not of you are behind).

Nidalee can be pretty strong in teamfights if you are pretty fed or have already good items.If you are really behind a Nidalee can be very useless in teamfights. So you have to decide in lategame where you want to splitpush or you want to group with your team. When you are really behind and your team can handle the enemy team it would be a better idea to splitpush on bot or toplane. But if you are very fed or something like that you should better group with your team to take objektives or kills to win the game

Nidalee has a really nice early/midgame because she can fight her lane opponent pretty good. If the laner roams much she can push towers fast with her attackspeed buff. The problem is Nidalee's teamfight because she has no cc. She is not that usefull like a Renekton or Jax in teamfights. But another pro is that when you win a teamfight you can give your Ad Carry the attackspeed buff and can push very fast towers or rush Baron Nashor.