Just finished playing as Jarvan and I wanted to upload this build for you guys.
Quick explanations:
Masteries - I didn't go along with the 21/9/0 or 21/0/9 fad. I just made what worked for me. Survivability plus dps. That's how it's going to work in my build.
Skills - Finish Golden Aegis first for the slow. The flat dmg shield is nice. Just be careful not to go below 300 intentionally. Great for towerdiving. With Demacian Standard all you need is the knockup ability and later the attack speed. Other than that you don't skill it for the dmg. Finally Dragon Strike has range. Try to put this straight through a creep wave for multiple last hits early game. Use it for knockup. Go wild. Cataclysm gives alot of face time with an enemy. Use this to chase and land the kill. The barrier is up for a while so I would suggest hitting with all your might, going all out.
Summoner Spells- I went for Ghost to catch up and run away. Exhaust has the same versatility. I would also suggest a Cleanse instead of an Exhaust. Purely preference. You will be stunned in your Cataclysm so I suggest you run some Mercury's Threads if you want to deal the max dmg.
Items- Take advantage of that passive and build a Madred's Bloodrazor. You'll need it. The boots are up to you. CC more? Get Mercury's Threads. Not that many CC's? Ninja Tabi. I personally like Mobility Boots. You are a ganking machine. Maximize that potential. Pwning? Grab Berserker's Greaves. All up to you. My item build maximizes attack speed and dmg. You need to grab one of the tankish items. Most likely Banshee's Veil but grab a Heart of Gold even if you aren't building Randuin's Omen. Sell it after 1.2 minutes for profit. Don't grab boots last btw. Get speed on your first trip back and finish when needed.
Runes- Basic DPS runes. Dodge runes are more expensive than attack speed runes so get whichever one you want. Both are viable. Heck take a mix of them. You need both.


WILL UPDATE SOON
-Naijtyr

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.


Jarvan IV extends his lance through his opponent, dealing physical damage and lowering their armor by a percentage for 3 seconds. If its lance contacts his standard it will pull Jarvan IV to its location, knocking up all enemies in his path.

Cooldown: 9 / 8 / 7 / 6 / 5 seconds.
Cost: 40 / 45 / 50 / 55 / 60 mana.
Physical Damage: 70 / 120 / 170 / 220 / 270 (+1.10 per bonus attack damage).
Armor Reduction: 10 / 14 / 18 / 22 / 26%.


Jarvan IV forges a shield protecting him from harm for 5 seconds and applying a 2 seconds slow to surrounding enemies upon activation. The shield adds more mitigation for every enemy champion nearby when activating.

Cooldown: 20 / 18 / 16 / 14 / 12 seconds.
Cost: 75 mana.
Damage Shielded: 50 / 100 / 150 / 200 / 250 (+20/25/30/35/40 per nearby enemy champion).
Slow: 15 / 20 / 25 / 30 / 35%.


(Passive): Grants Jarvan bonus attack speed and armor.
(Active): Jarvan IV throws a Demacian flag to a nearby area, dealing magic damage to enemies in the area and granting his passive benefits to nearby allies and again to himself for 8 seconds.

Cooldown: 12 seconds.
Magic Damage: 60 / 110 / 160 / 210 / 260 (+0.80 per ability power).
Armor Bonus: 10 / 14 / 18 / 22 / 26.
Attack Speed Bonus: 10 / 14 / 18 / 22 / 26%.


Jarvan IV heroically leaps to an enemy champion, dealing 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.

Cooldown: 120 / 105 / 90 seconds.
Cost: 100 / 125 / 150 mana.
Physical Damage: 200 / 350 / 500 (+1.50 per bonus attack damage).