Starting Items will be a Doran's Shield and 1Health Potion.To heal the damage done by hemorrhage.It will be DPS so using a similar HOT(heal over time) items can balance it out.

After you get 1.5k-2k gold in top lane.You should go back to base to get more items such as maybe Phage(to get more HP and AD also MS), BF Sword (to turn into IE because i use Infinity Edge on Garen a lot and nice damage to tanky champs), also boots to get to lane quicker since teleport is really valuable saves time from getting one lane to another or from base to lane.

MUST GET BLACK CLEAVER AS FIRST COMPLETE ITEM.Then turn the BF's Sword into an IE for more dmg since your Q and E can easily melt their armor and HP, and oh yea turn your boots into Boots of Swiftness for healing items.You will find out why in the next paragraph

ALWAYS GET A WARMOGS.So you can heal when trying to run away from Darius and can heal a lot if he is trying to chase so turning the tides can be easily done.(see this is why.Also getting Death's Dance might be crucial in team fights or soloing.Death Dance gives a lot of AD and Life Steal, the passive also synchronizes with Garen's E healing for 33%of AOE dmg and as you know the E does 1-2k dmg when its rank 5 with a few AD items.Fighting Darius using E will heal you a lot since 33% of 1-2k dmg is roughly about 300-500 which is just about the minimum damage his Ult deals so having IE is helpful more dmg = more heal!!!

For your last item you should get Randuins Omen.You should get that because of its passive which slows the attacker's Attack Speed by 15% and as you all might know.The more Darius hits you the more damage he does when he uses his ultimate and he can deal up to 1.75k true damage, I tried that in SandBox and I might be wrong because I didn't use crit items on Darius so it is not his max dmg he can deal.OK, guys thanks for reading my first guide tell me what I should work on and what is wrong with my build on the comment section.Also, don't forget to rate it if you liked it r hated it.