I have played AD Nid ever since AUG 2011 and have loved it from the minute I tried it. This build will allow you to 1vs1 almost any champion in the game. You will also be able to solo baron once the build is complete. You are ranged which will allow you to kill other champions, and when you need to chase hop into cougar form and chase em' down.

Most AD rune pages will work with AD nid, as she will regen hp with life steal and will have crit with the items she gets. Runes are entirely personal preference.

Masteries, like runes, are also personal preference, these are just the ones that I find most useful.

These items let you kill almost anybody and sometimes(without crowd control) 3v1, 4v1, and sometimes even 5v1 the other team!! I recommend building the boots first in case of needing the extra movement speed to get away or to chase other champions. If you do not need the movement I would then recommend getting zeal then full boots then finishing zeal into phantom dancer.

I choose my spear first in order to poke and sometimes get a long range first blood. If you want you can also get your heal first. Either way make sure to have 2 spears and 2 heals and 1 trap before level 6!

Exhaust, Ignite, and Flash are my recommendations. Smite if you want to roam/jungle at level 6.

Pros:

High damage output while ranged and melee
Cougar form "Q" does tons of damage
Human form "E" gives you attack speed
Human form "Q" still does lots of damage early into mid game as long as you level it up first

Cons:

Human Form "Q", "W", and "E" are AP not AD
Cougar Form "W" and "E" are both AP("W" is more for chasing and evading anyways)

I don't recommend straight jungling with Nid. I do like(in non-ranked games only) to put smite on and roam at level 6. This allows you to smite big jungle minions and easily gank for kills as your pounce in cougar form allows you to jump over walls and your cougar form doesnt take mana which lets you spam your abilities.

As with all AD builds, they cost SO much! Farming is one of the most important things in the game as Nid. Until you reach level 6(get cougar form) make sure to last hit every minion possible. Once you reach level 6 use your cougar form(no mana) to wreck minion waves throughout your game.

Use cougar form a lot because it costs no mana to you. Cougar form also gives you bonus Armor, Magic Resist, and Movement Speed. Almost always use cougar for chasing other champions because of the movement speed bonus that you receive.

Your passive is additional movement speed while in bushes. UNLESS YOU ARE FACING AN AP TEEMO !ALWAYS! WALK THROUGH BUSHES WHILE RUNNING AWAY OR CHASING!

You won't be disappointed with this full build, just try it! I wouldn't recommend trying this in a ranked game if it is your first game with this build. Try it in a bot game, then a normal game and then work your way up to ranked games!