This is a Tanky/Dps Build, you will have 4000+ hp and 200+ dmg when you buy all items, this will not make you immortal, but really strong and helpful in teamfights.
At the start you will be alot passive, but from lvl 10-11 you will start to be a beast, by killing enemies 1vs1 or at least 1vs2 without problems, and with your ultimate get like 3-4 assists in team fights.
Pros:
High Defense
High Damage
Demaciaaaaaaaaaaaaaaaaa
Nice Escape/chase mechanism
Cons:
Passive until lvl 10-11 (with this build)
Not easy to master the combination of skills
His ultimate if you dont know when to use can be fatal for you

My runes are in Armor penetration and health, you dont need more!
Glyph will help you to be more tanky early game. (so more attack damage with atma impaler)
Seals will help you to be more tanky late game. (so more attack damage with atma impaler)
Marks will help you to kill tanks easier, and not only them.
Quintessence Will help you at the start with alot of armor penetration in the begging (lvl 5-6) where if you meet a tank you can easly kill him.

Masteries i use 21/9/0, and i tell you why:
You dont need the 4% dmg reduction or something like that, you just need attack damage! with 4000hp and 200 armor you dont need anymore defense... and you can reach 400hp and 200 armor without any mastery... so use offense masteries!

CORE


- Doran's Shield: The best for start, Hp Armor and health regeneration will keep you alive for alot of time!


- Boots of swiftness: i always use this coz i need alot of movement speed to catch runner, the reason why i dont buy Mercury Threads or Ninja tabi is that they are useless to me, i can survive even without them, but if you have an heavy CC items get the Mercury Threads.

- Sunfire Cape: This will be hard to get, coz you have just Doran's shield and boots of swiftness, you should get it around lvl 9-10 and then you start to ROCK! you farm alot faster golds, you can tank some dmg.

-Warmong Armor : This gives HUGE amount of HP after you get this go fast to charge at his max, so when you will get the Atma impaler you will have 80+ attack damage bonus!

- Atma's Impaler : Combined with Warmong is The BEST 80+ attack damage 45 armor and 18% crt chance.

- Frozen Mallet: If you reach this point, its a really balanced match or they are closed in defense like turtles! with this you will incrase your bonus by Atma's impaler 25 attack damage that is good and you will Slow on each attack! NO MORE ESCAPE!

-Force of Nature : Get this if you have an hard caster team vs.

- Martial Cadence:(Passive)Jarvan IV's first attack on his target deals 10% of the target's current health as bonus magic damage, this caps at 400 damage. This effect cannot occur on the same target for 6 seconds.
- Dragon Strike:Jarvan IV extends his lance through his opponent, dealing 70 / 120 / 170 / 220 / 270 (+1.10 per bonus attack damage) physical damage and lowering their armor by 10 / 14 / 18 / 22 / 26% for 3 seconds. If its lance contacts his standard it will pull Jarvan IV to its location, knocking up all enemies in his path.

- Golden Aegis:Jarvan IV forges a shield protecting him 50 / 100 / 150 / 200 / 250 (+20/25/30/35/40 per nearby enemy champion) damage for 5 seconds and applying a 15 / 20 / 25 / 30 / 35% slow to surrounding enemies upon activation. The shield adds more mitigation for every enemy champion nearby when activating.

- Demacian Standard:(Passive): Grants Jarvan 10 / 14 / 18 / 22 / 26% bonus attack speed and 10 / 14 / 18 / 22 / 26 armor.

(Active): Jarvan IV throws a Demacian flag to a nearby area, dealing 60 / 110 / 160 / 210 / 260 (+0.80 per ability power) magic damage to enemies in the area and granting his passive benefits to nearby allies and again to himself for 8 seconds.

- Cataclysm:Jarvan IV heroically leaps to an enemy champion, dealing 200 / 350 / 500 (+1.50 per bonus attack damage) physical damage and creating a circle of impassable terrain around them for a 3.5 second duration. Jarvan IV can destroy the area by activating it again. Champions can still leave or enter the area by using teleport abilities.

Your combo should be E>Q>R>wait to finish the Ultimate and if isn't dead yet use W and E>Q.

First use your Demacian standard, then fast use your Dragon strike put it up in the air, after this your enemy should start running, if not go a little back so when you use your Cataclysm you can escape with your Demacian standard, if he hits hard use instantly your Golden Aegis, if not wait the Cataclysm end and if he is not dead use Golden aegis for slow and rotate again with demacian standard/dragon strike

Exhaust: The best, you can use it for Chase or Escape, and vs an autoattack champion like Tryndamere/Master yi = easy win!
Flash: i use Flash coz its the best to escape and gank.
Ghost : can be good too, pratically the same of Flash but i prefer flash for the istant SURPRISE!
Health: Can be good in some situations, but i dont advice it.

This is my first SERIOUS guide after the Veigar FLOP!
I hope you like it.