I'm looking for some help with Jayce. I'm relatively new to the game (reached level 30 but still under 100 total normal games; played vs AI to get leveled up) and looking for feedback.

I've been running 21/9/0 masteries and flat AD quints/reds, armor yellows and scaling MR blues. As for items, I tend to start boots + 3 pots or flask + pots + ward. I think pick up a Tear to eventually build into Muramana, Brutalizer, Vamp Scepter and then start working on finishing items up. I normally end with boots + muramana + bloodthirster + black cleaver + last whisper and one conditional item.

I'm doing lots of endgame damage but am getting pushed around a little in the laning phase and at all points in the game I get blown up real fast. In recent games I got my butt kicked by Kayle and then Nunu top with really no answer.

Should I be building more toward Trinity Force and Warmog's like a traditional bruiser or does that defeat Jayce's purpose? I feel like his hammer attacks are a little on the "meh" side and then I get nuked for having no survivability. Help out if you can. Thanks.

I don't play Jayce a lot, but you should definitely be getting some more survivability.

Maybe go with BT, BC, LW as your only damage items (or some other 3 item variant) and then go with boots and at least two survivability items conditional to the enemy team.

Obviously, if you're getting blown up, build more defense, and if you're doing just fine, build damage. I would say that BT and BC/LW are pretty important on him, and most AD champions for that matter. Muramana could be good on him, but I wouldn't know. If you do get muramana, then perhaps other mana items would be good as well, such as iceborn gauntlet/banshees.

Randuin's is almost always a strong item against AD with the passive, active, armor, and HP.
Bulwark wouldn't be a bad item to pick up if your team is lacking one.
GA is usually a pretty good item, but make sure to get HP to back up the resistances.
Warmog's/Frozen Mallet seem to be pretty popular now (especially warmogs) as they offer a lot of health.

For the most part, you're probably doing everything well enough, you just need to build a little differently so you don't get blown up. You'll do a lot more damage if you can survive another 10 seconds even if you give up a little damage.

As for laning, that will mostly just take practice and getting to know other champions. Nunu is just tough to beat, but he doesn't do as much later on in the games. Kayle, I'm not sure about, haven't really played much against her but I know her early damage is pretty high so watch out for that. Laning as Jayce involved a lot of poking and very little 1v1 dueling.
Remember, you don't have to get kills to do well. If you put your opponent behind and create an advantage for yourself in level/farm/towers then you're doing great.

Sample Builds:
- BT
- BC
- LW
- Randuin's
- Mercs
- GA/Bulwark/Wit's End?

or

- Trinity
- BT
- BC
- GA
- Warmogs
- Boots (mercs probably)

Way I play jayce you don't actually get into the middle of the team.

I run 21/9 with apen reds and ad quints arm yellows and mr/level blues (with 2 crit blues)
Build usually starts with some sort of sustain heavy top like flask+ sodas + wards or wards+ sodas
farm as much as you can, if you counter your lane opponent farm him
endgame my build is
BT+LW+GA+IE+SoTD+ some sort of shoes, usually ninja tabi. (SoTD not necessary but really funny)

Stay in the back and EQ the enemy team, if they initiate use your Hyper charge + SoTD to instagib someone, only go into hammer form to peel a bruiser off your carry for a bit or to finish opponents off.

IMO, GA + shoes are the only defensive items you need on jayce if you stay ranged most of the time.

U can build Jayce without defense. Start with - Crystalline Flask or Boots / Pots / Dorans's Blade / Tear / Brutalizer / Upgrade boots into Cooldown / upgrade Tear in Maramune / upgrade Brutalizer in Black Cleaver / Last Whisper / The Bloodthirster / Guardian Angel or Banshee's Veil or Frozen Heart or Iceborn Gauntlet. Good luck. Force your poke with Q, in team fights try to catch someone when they separate.