Jayce is a highly, HIGHLY, underrated champion. Honestly, he is actually pretty amazing. Good Nidalee player know (they should at least) that switching between ranged and melee is pretty awesome. But I keep seeing people build Jayce like a ranged AD carry. WHICH. IS. WRONG!!!

He is made to be bruiser. And not one of those At-Mogs bruisers. He's a new kind of bruiser, who can nuke carries and supports, go toe to toe with Darius, and down towers like a hero.

This build probably looks really weird. But before you down vote it, give it a quick try. You might even be pleasantly surprised!

[BTW, this is my first guide, so don't be too mean]

Runes

To be honest, Runes aren't the most important thing on this guy. I don't use Physical Damage runes on him. But the extra early game health and attack buff is really useful. Also, the armor lets you sustain a TON of early game abuse in top.

But like I said, runes aren't the most important thing. However DO NOT use Crit runes. They are really useless on him since all of his early damage comes from abilities.

My Suggestions are above, but you don't have to listen to me.

Masteries

Just a standard AD 21/0/9 works best. If you want, an armor based 9/21/0 or 0/21/9 also works relatively well. But the damage buffs should be what your looking for. Gotta think about the meta!

Now to the interesting bits.

That armor and 5 pots give you alot of lane sustain that is needed against other top laners like Irelia, Akali, and Shen.

The Phage is key. I've even built it before boots. It somehow amps your damage output to the max. Honestly, I really needed item early on. Plus it even gives you a slow and health, allowing for easy turret dives.

Boots of Swiftness are my choice of boots. They give you alot of mobility (because you need more of that) and are a nice boot to have. Alternatively, build Merc Treads or Tabi.

Trinity Force is a really stronk item. It boosts his AoE damage alot (1 to 1 AP scaling is nice). It also gives him boosted attack speed that is necessary mid-late game.
[NOTE] Start with Zeal then Sheen into Trinity

Aegis is A temporary item, but its cheap and gives your whole team an extra boost. If you don't think you need it, save the armor for the last item, or if you like Aegis, keep it and screw Thornmail.

Recurve Bow is a nice item to have during Mid Game. It fuels your Black Cleaver and Wits End really well.

Warmogs. Because you need moar health.

Wits End & Black Cleaver have incredible on-hit abilities. With these too, you melt everything. EVERYTHING!!!. Wits is situational. Sometimes, Ionic Spark or (if you are fed to all hell) Madreds Bloodrazer are better. But ALWAYS build that Recurve Bow into something.

At the end, you should drop Aegis for Thornmail. Thornmail is only if your against an AD heavy team (or 1 fed Caitlyn). If your against Alot of AP build FoN. If your against someone with stacking de-buffs like Vayne build Frozen Mallet. Or keep your Aegis, I don't care. But you will need one good armor/MR item.

The skill sequence doesn't really matter either. Just make sure you have all your abilities by level 3, and max your W last.

As for Summoner Spells, Teleport really nice on him. But the second spell is your choice. I hear ignite is all the rage in high ELO play.

Combat:

So Jayce can stomp most conventional top laners.

-Akali: When she junps, counter with your 'To the Skies' and knock her away, then switch the mercury cannon and do some pokin'. If she tries to hide in her shroud, stand in the middle with your AoE active.

-Irelia: When she jumps, remember that she just has that burst. You have more sustained damage. Just stay calm and use your abilities smartly. If she starts to be a serious problem, then knock her away.

-Gangplank: Ignore his parley and beat his face.

-Teemo: If you think he's stealthed somewhere, stand where you think he is, hit your AoE, and keep your finger hovering over your Q. Otherwise, your on your own.

-Shen: Don't push the lane, poke him with your range, and you should be fine.

-Darius: He's fine to beat into a pulp. If he pulls you in, switch to your melee and Q-E. If he doesn't back off, he'll get owned by your everything. Remember though that his blood stacks boost his attacks. Back out if your too low.

-Volibear: Make sure to pop his passive before you engage full on. Otherwise, he's in trouble.

-AP Tristana: You're boned >.<.

You don't have to like this build (or Jayce) but please give it(/him) a try. He is a really fun champion and it just damn cool.