Q stands for kill
garen is a tanky toplane fighter who's kit is mostly used like this.
Q to get close and deal some damage->E to shred enemies->R to finish of.
his W can be put in anywhere you want.
this build is based on making you Q about as destructive as your ult.
the combined force behind sterak and black cleaver would make for some nice damage but adding a trinity (who's spellblade effect makes your next attack 2x as strong) and the dead man's plate makes your Q an attack that wil desimate most adc/mages and assasins.
the new order is: Q for getting close and dealing tons of damage->W for some extra damage if your ult can't already finish the job->ult to finish the job.