This Jayce is a bruiser he will become really hard for an adc to take down because of his aggression and ability to take a beating. Fire shock blast through your acceleration gate to lead, followed by to the skies, then run in front of enemy while they are slowed smashing them towards your turret after doing so switch into ranged mode and fire a shock blast. Congrats you just got a kill.
For the second build don't be as aggressive you wont have as much health but you'll do way more damage a lot faster.
I prefer build one because of it's tankiness it allows Jayce to escape very easily when need be. And allows him to take on more than one person at a time but wont kill very fast giving the rest of their team time to show up.
Build 2 doesn't have the tankiness but can kill 1v1 very easily with no worries of gank because of his shear speed of killing.