you should spec 1-19-10 or 1-21-8 if you are tanking.

cloth armor + 5hp pots
HoG+boots
finish mercs
go straight for randuins or BV depending on other team
get whichever one you didnt get

thats pretty much the core for a tank udyr imo.
after that you can get offensive items if you're facerolling, or get further tank items.

for runes I run arpen reds, flat armor yellows, scaling MR blues, and flat HP quints.

wow, strangely thats almost EXACTLY what i run, but an alternate thing u can do for a slightly less tanky udyr

(if you go pheonix lvl 1, turtle, lvl 2 and 3, you have plenty of hp at lizard only with 2 pots-saving some cash, after doing golem your 4 (with exp from utility) and then u can get bear and gank

if you only buy 2 pots, and successfully gank you can make the lifesteal jungle item, if gank fails you still have enough for madreds atleast

making madreds imo makes u faster jungle if u decide to jungle into mid-late (which there is a branch-off for if you decide to go for gank/lane control)

if you go for the latter, randuins and tanky items better like he said, making the HoG, but if you decide to jungle into late getting a madreds into lifesteal item keeps u up to momemntum allowing you to control jungle on both sides better (benefit of ward, plus smite for steals)

i do same runes but i have questioned it myself, is armor pen better than magic pen? (i use armor pen cause udyr's stat on base atk dmg looks high)

I suggest instead of ArP reds, use mP reds. I find that phoenix hits a little bit harder while jungling with it.

ArP marks
armor seals
mp5/lvl glyphs
HP quints

would this be the rune setup for a jungle udyr?

@PardonMySwag: that shouldn't improve jungling since most creeps dont have magic resist.

With my jungling Udyr, I run Arpen Marks, Dodge seals, MR/lvl glyphs, and HP quints, but I usually run back to base as soon as I can get my Heart of Gold.
I think that with Aspd runes and turtle, you can do the whole jungle, but I never tried it, I have no more IP for that :/
Could someone tell me is it does work ?

For red's I would suggest attack speed, which are at the least equivalent to arpen/mpen since they're nerfs but will allow you to make the most of phoenix proc and still get oomph out of turlte, and faster bear stun chaining in team fights.

I'm using Asped reds and quints atm but if you mean dragon as well, i generally go for a gank instead, after a whole jungle clear i'm only level 4 and i could only do dragon then if I had my mandred's blue buff and a potion or 2