Aram jayce should be played only 1 way, as an AD poke monster

Attack Damage Runes, some defence

AD masteries, get Sorcery instead of Fury for CD Reduction to spam E-Q combo more often

Tears first to spam E-Q combo, Long sword for damage.
Last whisper to maximize damage with E-Q poke.
Balance damage & defence as necessary.

Max Q first, poke harder with E-Q combo.
Then max E, for bursting with Thundering Blow.
Lastly max W, for right clicks when Jayce's late game right click hurts.
Take ult whenever you can.