This Jarvan build will enable you do deal heavy damage early and will provide the tanky attributes that make him so scary late game. This is just how i have built him and found to be effective in the short amount of time hes been released. This build is a work in progress and and definitely still tweaking it. any constructive opinions or tips. feel free to comment and let me know

The runes i chose for Jarvan are 9 armor penetration marks, 9 armor seals, 9 magic resist glyphs, and 3 armor pen quints. these runes really strengthen jarvans early game. its gives you a lot of armor pen to take down opponents for an easy first blood. also allows you to fight more early with the armor and magic resistance.

i go with a simple 21 9 0 build for masteries. simple. it gives him all the attack you want in him to rack up kills and adds some defensive help as well.

I decided to go for some attack damage early and build on the survivability late game. i grab boots of swiftness because i love the all around speed it gives you. you could just as easily go with mercury threads depending on the opponents you have. also you could possibly grab beserkers greaves. I like the boots of swiftness.
then i go for the bloodthirster, it gives me some lifesteal which is extremely helpful and it heavily increases my damage output.
the next item i go for is the sunfire cape. this is a great item for jarvan. it gives you more health. some armor, and it is so compatible with jarvan because in most fights your going to be in close quaters with most of the other team. especially when you use catacylsm, your enemies are locked in next to you and that 40 magic damage per second is invaluable.
i then grab the last whisper for the armor pen, but depending on how your doing you could wait on this one and grab banshees veil first. the armor pen in last whisper is amazing. really really increases your damage output.
after this you could grab either more armor, maybe thornmail, or you could go towards more damage and take frozen mallet for the slow it gives you, your enemies will not be able to escape from you. with your high speed in boots of swiftness, you can easily chase them down, along with your spear jump combo, and cataclysm. and all the while your dealing extra magic damage with sunfire cape. a sick combo!

with your high armor pen early. i like to take dragon strike early, taking an early point in both demacian standard and golden aegis. then leveling up dragon strike until i can get cataclysm. then finishing off dragon strike then alternating and finishing up demacian standard and golden aegis. jarvans skills are amazing.
Dragon Strike is a great harass move especially when used along with demacian standard. its also your heaviest damage output move.
Demecian Standard is great, you drop a flag on an opponent dealing damage, as well as increasing your attack speed and armor within a certain range of the flag. this skill is great for team fights because it grants the same boost to nearby allies.
golden aegis is amazing. grants u an extra shield of bonus health also some additional armor. this move has saved me several times. great for escaping and surviving ganks.
catacylsm the reason why jarvan is all the rage with his release, this ultimate is amazing when used properly. he jumps, land on opponent, deals damage and encases them inside a ring earth for a few seconds. you have to be aware of who to use this move on because almost any escape move can be used to get out of the ring. any champion with a jump or a dash or teleport move will be able to escape. so be very careful you dont waste this. also check to see who on the other team has flash, and dont use it if they have flash available. when used right cataclysm can finish off the last opponent for the ace, or win an entire team fight when placed well, blocking of melee champions from the rest of your team while feasting on their squishies.
jarvans combo. your drop demcian standard, then dragon strike to the flag, lifting ur opponent in air and dealing heavy damage, while their in the air go ahead and use golden aegies, they land auto attack em, using ur passive( first hit deals 10% their current health in magic damage) then repeat moves. use catacylsm if necessary. this combo is very effective as harrass early game as well.

i started off using ghost and exhaust with jarvan but when i started getting boots of swiftness i dropped ghost for ignite. i love ignite on almost any melee or assasin champion. its so effective and can help get early game kills so well.

this is my tanky assasin jarvan build. i have found this build to be very succesful and it just makes him such a scary champ. when your using him right he can easily take on 2 champs alone, maybe even three. any suggestions or constructive feedback feel free to let me know. thanks!