Okay. This is my first build on here but I like using this if im playing tanky and supportive. To some it might be boring but its quite fun to win with this build. This is how i like to play nunu. He has enough survivability so i like putting those AP items for damage.

Nunu might be a good champ for you to buy because he is cheap and not too hard to play. But he is good on all levels of play.

LETS MAKE TRACKS

Pros-
-so much survivability (3000+ health?)
-will not die much (use your Q)
-Helps your team alot in team fights
-can do quite some damage
-is only 450 IP if your new or dont have him

Cons-
-some think boring
-doesnt have crazy damage but its supportive and sufficient

Lets explain these skills!
Visionary.

-Every 7th melee attack makes the next ability cost no mana. (not too important but super helpful in early and mid game)

Consume.

-Eats any minion and heals you for alot. this give you alot of sustainability(and the ability to jungle)

Blood Boil.

-Gives you an amazing attack speed and movement speed buff. Good for pushing those lanes or catching up to an enemy.
ADVICE: Place it on a teammate and you BOTH will get the buff.Preferably melee dps.

Ice Blast.

-Main damage source. Does damages PLUS a 1:! AP ratio so it hits for alot. AND it has an awesome slow.

Absolute Zero.

-Good Ultimate. Its called that because it leaves them at ABSOLUTE ZERO HEALTH(stole that joke from another build lol). anyways its awesome with a 2.5:1 AP ratio! Can easily slow and one shot squishies. It helps and does alot of damage in team fights.

Items are pretty self explainitory.
you will have boatloads of health and decent damage output.
you can go a different start item but this is what i like.

I like starting out with the null-magic mantle and 2 H pots.
you might say health pots? nunu his Q?
but the are wonderful if you get in a fight early on and put a point in my E instead of my Q because its better for damage and harass(you have a slow!)

The other items are a balance of AP and survivability

6TH item
-Warmogs (for tons of health
-Guardians Angel (for armor MR and that revive)
-Thornmail (if they Have alot of physical damage)
-Another Deathcap? (for that super nuke)

I like these spells on him but you are definently free to try new things.
Heal could be replaced with flash or something.
I LOVE teleport because you can be back in lane fast or support teammates faster!

Also i think ghost or exhaust is a bad choice for nunu because you have your W(for movement speed) and your E(for slow)

Defensive stuff (no need to explain) and i go those 9 extra points in offensive for a little nicer damage.
Ultility would be a good tree also with a little more sustainability.

I do not know much about runes at all but these seem Good for a little more damage and to shred some tanks.
The health quints are quite nice early game for their cost too.

You are a tank, mostly. if you dont have a team your role can be useless
COMMUNICATE alot. It helps

You have enough ap to do some serious damage and you have lots of health.

I think that is all. Thank you for reading my build and i would like some feedback. :)