This guide isn't finished. So I will upgrade/improve it in a few days.

First, here are the pro/cons of playing top Nidalee for lazy readers before testing her:

Pros:
+ Ranged AD, so you can harass all those melee champs that usualy go top.
+ Sustain with E.
+ Traps that work as wards.
+ An ultimate that changes all skills and the campion itself.
+ AP and AD scaling.

Cons:
- No CC.
- Easy avoidable traps.
- Tricky passive and ultimate
- Your teammates will se you as "support" rather than top.
- His "burst" skill, the Q spear, can be avoided plus doesn't scale with AD.

Like a lots of champions, there isn't "The rune page for Nidalee" Here are some changes that you can do:
Reds/Marks: Attack damage, if you find hard to last hit the minions.
Yellows/Seals: Armor are great against a lot of top players. Mana regen can be a choice, but will be useless with the catform, plus you won't be spamming spells.
Blues/Glyphs: Ability power is a choice, make sure you hit some spears. Attack speed is another choice, but not my fav.
Quints: Flat AD are great for bruiser, even flat health ones. You can try AP quints + AP glyphs, and go for a item build AP-free.

Feel free to take whatever your playstyle needs.

Like runes, that's the page I use for Nidalee, but feel free to change it. You can go 9 21 0 for extra tankyness, or avoid AP masteries for more sustain or damage.

Prowl(Innate): Moving through brush increases Nidalee's movement speed by 15%. The buff lasts for an additional 2 seconds after leaving brush.

The passive is not like Morgana/Nasus (spell vamp and life steal) So that means you can't forget this passive. Why? If you are trying to escape a gank, go for the brushes. If you wanto to harass, brushes. If you want to go back to the lane a little bit quicker, brushes. So, don't forget, brushes are your friends!

Javelin toss Q (Active): Nidalee tosses her javelin, dealing magic damage on impact that increases depending on the distance between Nidalee and the target at the time it is hit. The multiplier caps at 2.5.
Cooldown: 6 seconds
Cost: 50 / 60 / 70 / 80 / 90 mana
Minimum Damage: 55 / 95 / 140 / 185 / 230 (+0.65 per ability power)
Maximum Damage: 138 / 238 / 350 / 463 / 575 (+1.625 per ability power)

This skill is butter and bread for a pesky AP Nidalee, but that doesn't mean isn't useful for a bruiser/AD Nidalee. You can get kills, harass, and even check brushes (if you hear the sound of hitting, then someone is in there) This skill and the W in catform are the ones that are worth getting some AP.

Bushwack W (Active): Nidalee lays a trap that deals magic damage over 2 seconds when sprung by an enemy, revealing them and reducing their armor and magic resistance for 12 seconds. Traps last for 4 minutes.

Cooldown: 18 seconds
Cost: 60 / 75 / 90 / 105 / 120 mana
Total Magic Damage: 80 / 125 / 170 / 215 / 260 (+0.4 per ability power)
Armor & Magic Resist Reduction: 20 / 25 / 30 / 35 / 40%

I usually take this skill first, then I put some traps in the bushes, and then B. After that, I puto some points in W at later levels. The damage and amor/magic res reduction can kill a dying champion who wanders in the wrong place, but 99% of the games, will be like "free" wards.

Primal Surge (Active): Nidalee heals an ally champion and grants them bonus attack speed for 7 seconds.

Cooldown: 10 seconds
Cost: 60 / 80 / 100 / 120 / 140 mana
Heal: 50 / 85 / 120 / 155 / 190 (+0.7 per ability power)
Attack Speed: 20 / 30 / 40 / 50 / 60%

Your sustain skill, plus you can heal an ally and save his/her ***, and has an attack speed buff. You can use it to harass beter, or use it on your range AD mate to destroy towers or get dragon quicker.

Aspect of the cougar R (Toggle): Nidalee transforms herself into a cougar, and in the process gaining a new set of abilities, bonus armor, magic resistance and 20 movement speed.

Nidalee loses 425 range while using this ability.
No cost
Cooldown: 4 seconds
Bonus Armor & Magic Resistance: 10 / 20 / 30
Each additional rank increases the effectiveness of Nidalee's cougar abilities.

The skill that definies Nidalee. This will change you into a cougar (wink wink) and the skills you had, and giving you armor and magic resistance. Every time you level this skill, the catform skills will get better. Remember that you won't be able to do ranged attacks neither use your normal skills. All the skills in catform are FREE.

Takedown Q (Active): Nidalee's next attack will be enhanced to deal additional physical damage plus increased damage based on how low her opponents health is to a maximum of 300% physical damage.
No cost
Cooldown: 5 seconds
Minimum Damage: 40 / 70 / 100 (+1.0 per attack damage)
Maximum Damage: 120 / 210 / 300 (+3.0 per attack damage)

This skill can finish a low HP enemy, and the scaling is pretty good. But you will need to be in melee range to do it, so use passive/W in catform to get a hit. Remember, it will do more damage the lower the health of the target is.

Pounce W (Active): Nidalee lunges forward, dealing magic damage to enemies around her landing area.

No cost
Cooldown: 3.5 seconds
Jump range: 375 (estimate)
Magic Damage: 125 / 175 / 225 (+0.4 per ability power)

This skill will allow you to:
+ Get closer to the enemy
+ Avoid a gank, getting away from an enemy
+ Move faster to your lan/ gank someone.
+ Jump some walls.

Pretty neat. Like all the cougar skills, you can spam them since they cost nothing. Now, remember, YOU CAN'T JUMP OVER ALL THE WALLS. Also, you will pounce in the direction Nidalee is moving, so it can be tricky to do it.

Swipe E(Active): Nidalee claws at enemies in a cone in front of her, dealing magic damage.

No cost
Cooldown: 6 seconds
Cone width: 180 degrees (estimate)
Magic Damage: 150 / 225 / 300 (+0.4 per ability power)

Some area damage, great for cleaning minions. Also, I use this skill first then Q to the enemy champion, so I deal a little bit more of damage. As every cougar skill, has no mana cost, so feel free to spam.

Ghost OR Flash

Ghost will allow you to chase enemies better, and avoid ganks. With the passive and the W in cougar-mode, you can escape. Flash will allow you to jump the walls you can't avoid with the W in cat form, plus get the killing blow. Choose what suits you better.

Ignite or Teleport

Iginite can finish an enemy champion, so it's useful at early. However, in late in somewhat useless, since the enemy champions will have a lot of health (like the enemy top) Laning against a Teemo, got 3 kills thanks to ignite. Remember that early kills mean a snowball effect. Teleport is great in early-mid, in late will be useful when you do a B with low health after a teamfight, and will allow you to keep pushing that tower. In early, use it go back to your lane so you don't lose creeps. Also, with some wards, you can gank other lanes, or after ganking (usually bot) going back to top.

Starting item + 3 x
Use it against weak champions. Nasus needs to get harassed early game, this will allow you to go in/out of the brushes and hit him with your autoattacks.

+ 5 x
Use it against early agressive champions, usually those who have poke abilities. Gnagplank can harass you with his Q, so, the extra armor + sustain will come in handy.

Pick one of the choices above. Those two starter items are useful in every build. You need to buy boots, and the cloth armor can be uprageded into a lot of things that are useful (Wriggles, Guardian Angel, Ninja Tabi, Aegis...)

Now, the next are possible choices, but these items will force you to follow a path, or will even be bad choices against certain champions.

The usual starter items for AD in bot can be useful. Gives you all-round stats, but you will lack armor and movement, plus you won't get any pots and you will rely on mana/E spell. If you have plain AD runes, don't get this item. Later, I will discuss when to get this item.

Plus a potion. This can be built into Phage, Brutalizer and Madred's/Wriggles. The problem is, it doesn't give that much damage, you only have 1 potion, and this will force you to get some of the above. It's an option, but IMO, there are better items.

Plus a potion. Someone will say "WUT?" This item is a choice if you're solo against two, if the enemy doesn't have a jungle. The rule is going with a jungler and solotop, but sometimes you will face this situation, when they can harass/push you out of the lane. Build into philo's, and you will have enought sustain/GP5 to do nice in your lane. As I said, only get these against 2. BUT, if you can handle the situation, go for cloth armor or boots.

This can be a choice. You have AP scaling, so the Q/spear will be more effective. The problem is, you will need to sell this. The other problem, most of the damage you are gonna deal, is physical. We want to harass the enemy with autoattacks to make him go B or get a kill. The spear can be dodged, avoided with minions. AND it costs mana, so you will run out of mana eventually, and you need that to stay more in lane/win trades with your heal.

Item builds
Now, these are the builds you can go for. In the next chapter, I will discuss what to get depending on the situation.
NOTE: The boots are ninja tabi, BUT this won't work againts every enemy team. Go mercury treads if they have dual AP (mid and top) or triple (junglers like Fiddle) and if they have lot's of CC (Maokai, Sion, Vayne, Alistar, Pantheon...)

THE SIXTH ITEM FOR TANKY:
More damage More tankyness