Thor S3 Jungle

breastplate or mantle are a good way to get to, or near to, max cooldown. Brawlers is there for if you are against a healer and are not being bursted. Take breastplate if you are against high physical dps and take mantle if you are against high magical dps. If they are pulling a crazy 4 magical dps comp then bulwark is an early option here.

Titans gives a lot of power and pen for very little gold and bulwark is just a plain good magical prot item.

Your last item is super situational. I usually find it best to go defense last, and these were the items i had most success with. I mostly take midguardian but if they have a character that has tons of lifesteal late ,e.g. Fenrir who is very common atm, spectral will help you to deal with them without them being able to heal for more than you are damaging them while you have a 30% chance to take less damage from them. But as i said this slot can be taken by whatever you feel comfortable with, these are just my personal favorites.

If you are against a character that can cancel your 3 easily, e.g. serqet, you might want to consider maxing your 1 first, especially if you are comfortable with free hand double taps. You don't really need to max your ulti until late as it is mostly just there as utility for ganking and fighting, to help you get your other abilities off.