First guide ever. I'm going to make a talon one next.

First off, I started off as a Phoenix Udyr cause the guides said it was better/faster. Now that I have been playing Udyr a lot recently, this is how I tend to build him when I play. This is a Tiger guide, and certainly it is a lot slower than Phoenix, but I like tiger a lot better. Why?
Because when you hit large targets (for example: a 6 stack chogath, dragon, baron) it looks really freaking cool. Yeah, that and you claw down enemies like nobodies business.

I roll with Ghost and Smite.

Ghost - run through minions + boost in movement speed stacks well with bear form, and it will keep you on your target as they try to run away.
Smite - you need it to jungle effectively, anyone who doesn't bring it is a dummy. Except shaco. I hate shaco.

Optional:
Flash - Gap closer/escape. Too bad most enemies will outrun/get away since you don't move fast enough.
Cleanse - Never used it, but can be a good replacement for merc treads to get boots of mobility/swiftness instead.

Everything else is ****.

I usually go 0/21/9 or you can go 0/20/10 for the extra duration, but I found that the 4% defense saves an extra HP pot after the first go through of the jungle + you gotta go back sometime so part of the buff is wasted anywhoo.

Red: ArPen
Yellow: Flat Armor
Blue: MRes/Atkspeed
Purple: ArPen Quints

Armor Penetration for killing the jungle creeps, and enemy champs fast. Armor for the extra defense against auto attacks/jungle creeps, MRes for those enemy champs that do magic, or go for a minimal 6.4% in attack speed if you have those runes.

I know that you're going to do a fair amount of magic damage in this build due to the bloodrazor, but it always helps to have a good amount of physical mixed in as well.

Tiger - Bread and butter of this build. The DoT (damage over time) is like 500 at level 5, and you will cast it every couple of seconds.
Turtle - Mana regeneration, life steal, and a SHIELD. Don't underestimate the shield, it WILL mitigate a TON of damage. Its like having a couple extra HUNDRED HP.
Bear - Boost in movement speed for 2 seconds at max rank, and a stun every 6 seconds on an enemy.

Start off with: Cloth + 5 pot, a staple for many junglers. Go to blue and get your team to PROTECT YOUR JUNGLE. You don't need a leash if you have all the runes/masteries, but it can save a pot or two.

Blue > Wolves > Wraiths > Red > 2Golems

Smite blue, smite red. It might be tempting to finish wraiths quickly by smiting big wraith, but tiger/turtle do short work of him without taking too much mana anyways.

Once you go through your first run, you can either start ganking or B and get boots + ward/2pot.
Ward + 2 pot is suggested if enemy has a jungler. Ward top lane so that they don't have to, and they can focus on getting whatever items they need. Otherwise, grab a mana pot cause your blue is gone.

You MUST gank after getting your boots, because you still have your red buff up. Bear + Ghost will most definitely get you a kill or two depending on how your team is doing.

Once you get your claws, you can either decide to get a wriggles or go straight to the bloodrazor.

Wriggles will help you steal enemy jungle creeps faster, ward dragon, take dragon quickly as well as the lifesteal will keep you in the field FOREVER. But you will be hard pressed to kill enemy champs.

Bloodrazor - since youre going tiger anyway, youre going to be attacking FAST, what better to use than an item that does a percent of their health. You kill squishies in seconds, and tanks will fear you because they stacked armor instead of MRes. But the jungle will still hurt though.

If you manage the time to get both (you fed fatty), take your main tank, and AD carry to go on their merry way to kill baron.

On building bloodrazor:
Pickaxe first - more damage for every hit you do while killing someone.
Bow next - the 40% is impressive, only if you're hitting them and not moving around.

On merc treads:
Get these ASAP, after wriggles, or before building the bow on bloodrazor. CC will shut you down completely. Turtle will save your life if you towerdive, but you wont be able to activate it if you're silenced/stunned. You have no gap closers/escape, if they root you.

Next up after these two core items are: Trinity , Randouins , Force of Nature , Guardian Angel.

Trinity gives movement, damage, atkspeed, ap for shield, possible slow, crits, everything you want on an item. Great synergy for all your forms.

Warden/Randouins works well against everyone, aoe slow, when hit atkspeed reduction/slow. If you were running, you will get away, if you were attacking, they wont get away. You win either way.

Force of Nature, movement speed + insane health regen + AP casters do about 40% less damage. Never need go back to base.

Guardian Angel, die, come back to life. Not as awesome as the other 3, but it has its uses.

If you do manage to get all these items, you can pretty much solo their base without minion assistance.