This is my Jayce Build it was very usefull for me and I was glad to share it.
I will discuss a lot of things(for me).

Armed with wit, charm, and his signature transforming hammer, Jayce lives to protect his native Piltover. Long before his nation called him a hero, however, he was a promising young inventor. When Piltover commissioned him to study a rare arcane crystal, Jayce discovered it could be used as a vast energy source. Eager to make a name for himself, he began developing a device to harness its power. Word of the crystal's potential reached beyond the borders of Piltover.

Viktor, the machine-augmented scientist from Zaun, brought Jayce an offer – together, they could use the crystal to advance his "glorious evolution," a vision of humanity fused with technology. Jayce refused, but the Zaunite had no intention of leaving empty handed. He effortlessly blasted Jayce aside and seized the crystal, incinerating the lab's meager security force as he left for Zaun. Jayce implored the Piltover government to respond, but the officials refused to support an act of aggression. He decided to act alone, realizing that if no one struck back, Piltover would never be safe.
Jayce returned to the lab to prepare for his attack. After intense research, development, and hands-on testing, he emerged with his crowning achievement –the Mercury Hammer. Weapon in hand, Jayce marched to Zaun and began his one-man assault. Viktor's acolytes rushed to stop him, but Jayce smashed them aside, fighting his way into the heart of the lab. Inside, Jayce saw the horrifying brilliance of Viktor's creations, all powered by the energy of the arcane crystal. He realized that his only option was to destroy the power source, but Viktor stood in his way. Though their clash left both scientists heavily wounded, Jayce managed a desperate strike at the crystal. He shattered it and escaped as Viktor's machines erupted in flames. When he returned home, exhausted but victorious, the citizens of Piltover hailed Jayce as a hero. He reveled in the adoration, but knew that his actions had drawn the attention of dangerous enemies. Now devoted to the defense of his people, Jayce is Piltover's best hope for a bright future.

"Trust me: if we're smart, Piltover can stand strong against any threat. Hey, I'm living proof."
―Jayce

these runes are for the early heavy damage because of the penetration.
I did the runes for armor for dealing with ad champs early like Fiora & Gangplank

Items like FrozenHeart are good for slowing the enemy while dealing heavy damage to them.i chose these items so you can carry your team in team fights and save them at all cost if they worth it

Don't they look normal. The reason why I choose the LightnigField is because it deals the most damage. I made them in this position so everyone one can play good.

What's more fantastic than going faster than the speed of light with Jayce well don't wait anymore because the gate & Ghost will bring it for you for the fast gank and back to lane attack also used with Rammus I hope this was usefull.

I'm not used to this section but i will try.

Pros.
+ Quick damage
+ Quick Lane ganking
+ Slow enemy for helping teammates


Cons.
- You will be focused
- Come on your Jayce who doesn't run from you when your stunned.
- Not much CC's for team thats why the FrozenMallet.

I had fun making this here's a random Defender