Chaac Solo | Season 11 | Patch 11.1

Blue Stone, Transcendence, and Gladiator Shield are the three main portions of the build to get you winning early and late game.
Blue Stone gives you nice early clear and helps evolve Transcendence quickly which gives you a nice boost to power and mana. Chaac abuses the Gladiator's Shield's passive for massive late game damage.

Starters
Bluestone is the significantly best option for Chaac. You will get better clear early and mid game from the Bluestone.
Teleport Fragment first for easily returning to lane and it's also great for returning to solo lane after ganking with the duo lane teleport.
Golden Shard is useful for clearing the xp camp and blue bluff at the start of the game. But the Horn Shard is a nice alternative that can be used effectively all the way until you upgrade it at level 12.
Two health pots so that you can be full health when you reach lane after clearing xp camp and blue buff.

Item #1
Transcendence is a must buy. Do not skip this item. Chaac benefits massively from this items passive and your build will suffer without it. Build high mana early to maximize its damage.

Item #2
Choosing a protection item with high mana is essential to get the most out of your Transcendence's passive effect because having high mana early game can ramp it's damage potential very quickly.
Breastplate of Valor is a very easy choice for this, in addition, the Breastplate of Determination glyph helps you max out your protections in the late game.

Item #3
Sekhmet's Scepter goes well with Chaac's third ability, the slow allows you to stay in range to get your hits in so that the Scepter's passive can proc and allows you to chase better guaranteeing kills when the enemy is low and allowing you to stay in the fight longer. It combos well with the Breastplate of Regrowth, but its not necessary, because having the Scepter as your only heal proc works well on its own.
Dawnbringer is a nice pick if you prefer early team fights, and is always great to have as it makes your late game fights more potent.
Runeforged Hammer works well with your ultimate ability as long as your casting it early in the fight, having them silenced (and slowed with your third ability) helps prevent the enemy from escaping the runic symbol's range.
The Executioner is nice if you prefer to be extremely aggressive, or are expecting lots of ganks. Chaac doesn't benefit from basic attacks as much as he can with his abilities so its best to only build one such item and maximize your damage output after the protection reduction applies with other ability damage items later in the build.

Item #4
Gladiator's Shield is a must buy. Do not skip this item. Chaac benefits massively from this items passive and your build will suffer without it.
If your close to an enemy, try using your second ability before throwing your first out. You'll not only protect your self but buff the Gladiator's Shield's damage output.
You can build Gladiator's Shield last if you would prefer getting more protection items before it. But try not building it too early as you wont have very high protections earlier in the game.

Item #5
The last item in the build is the least important. Use this slot to build an ultimate buffing item such as Pridwen or Dawnbringer if you dont have one yet. If you do have one already, buy a situational item to either buff your team, or debuff the enemy team instead. Preferably build protection items to enable your Gladiator's Shield.
Pridwin does similar to the benefits you get from Dawnbreaker, but building Pridwin in the last slot is nice for its additional protections.
Archdruid's Fury combos very well with the rest of the items to get large amounts of high burst damage.

Finished Build
After you finish your items, get the Breastplate of Determination first, than the Glorious Pridwen. Always get Bluestone Brooch as soon as you hit level 20.

Ability one is Chaac's best ability. Try to proc his passive with it to be able to cast it as much as possible.
His ultimate should be upgraded as soon as possible to maximize it's effectiveness.
Ability two has the next most priority because you want to have as many protections as possible once your have Gladiator's Shield built.
The third ability is more effectively used to slow enemies and proc items than it is as a healing source. It only needs to be upgraded for cooldown.