Resistances are completely moot once preseason hits stick to HP and Damage instead

There are a few reasons why both armor and magic resist Are completely moot.

1. The gold efficiency or basically the worth of these stats from items and runes is half and in many cases less then that of he value you get out of offensive runes or items
2. They get penetrated losing even more value over time
3. You have to build vs multiple damage types, an enemy can stack up 6 efficient offensive items and you are stuck building half as many half as efficient items that at a certain point lose half their value on top of that it's really shooting yourself in the foot if you build any serious defense
4. With the new adaptive damage after the new rune system gets implemented you even risk losing all your value on your resistances because your enemy swapped damage type

What you can do, is simply stick to building health as this helps fend off all types of damage Items such as

Besides health it will be better to build offense as it has so many advantages over defensive items and many of the offensive items also have some of the most powerful defenses so if you need some bulk just use those items Stuff like

This doesn't mean you should never build defensive items, it just means you should heaviliy limit them and just stick to a maximum of 2 or so which best counter your opponent

things like

grab your warmogs grab your defensive item and otherwise stick to damage

Your defense is moot but so is theirs

Also forget about the resolve path it gives inferior early game stats and forces you to use one runeslot for a set of inferior runes with the rest of the choices all being pretty weak compared to other rune paths

simply stick to the other paths

And don't forget, stick to building health first or you are going to get screwed over hard by adaptive damage in the midgame and you will lose out vs pen in the late game just get hp instead and just wait out the adaptive damage swap before you actually start building resistances and then just build 1 or so to make penetration less harsh Beyond that build damage and health so you can kill them faster so you wont have to tank as much