3.15 - Chieftain RF tank

https://pastebin.com/4671vZgb

N: Ramako, Sun's Light - C: Tasalio, Cleansing Water - M: Valako, Storm's Embrace - E: Arohongui, Moon's Prescence.

Helmet: Vaal RF - IncAoe - Efficacy - Ele Focus - Conc Effect (helm) - Burning Dmg (Helm)
Shield: Decoy Totem - Dash - Infernal Cry
Boots: Vitality - Summon Skitterbots - Purity of Fire - Arctic Armour
Gloves: Scorching Ray - Controlled Destruction - Infused Channelling - Swift Affliction
Scepter - Storm Brand (lvl1) - Increased Critical Strikes - Immortal Call

Use a Scepter with the highest elemental damage implicit possible and the 2 mods needed are +1 Fire Skill Gems and Fire Damage over time multiplier. If you can also get or craft on it high increased Fire Damage the better. Cost around 1 ex but you can get cheaper with only fire multiplier and some other useful stat like fire damage, damage over time multiplier or burning or elemental damage until you can upgrade.

Absolutely needed: Kaom's Heart and an Elder helmet with the mods Socketed Gems are supported by lvl 18 - 20 Conc Effect and lvl 18 - 20 Burning Damage.
Replica Atziri's Foible as soon as you can get it. It's around 50c a decent roll, maybe less you can get a bad rolled one much cheaper to level and later upgrade. A much more expensive and more damage oriented variant is to use a Hunter influenced Marble Amulet with +1 fire gems and damage over time multiplier, craft the Aoe mod on it with some decent life and regen mods.

For leveling start with Fireball or Molten Strike, Flame Totem and if you can get Flame Wall too. Use Springleaf and 2 Kikazaru Rings, you need your Fire Res capped, Vitality aura and the amulet. If you can't get the amulet yet you can use other good regen low level amulets like Araku Tiki, or try using life flasks for sustaining RF but otherwise delay RF use and just level with Scorching Ray and Vaal RF. Later when you get your regen high enough you can drop Springleaf for Saffell's Frame.
Try to get all your resistances including Chaos res over capped, I have like 40% Chaos Res and reach almost cap with Flask. I was overcapping it but decided to craft more damage with non vaal skills during soul gain prevention which helps on bosses a lot.

RF builds need character and gem levels to start feeling they are working and the more life you have the more damage you get so focus on high life rolls and elemental rolls on jewelry.
You can use Vermillion Rings but Opals will be more damage.

I am currently using very cheap gear, the only expensive items I have are my rare boots 1ex and my Scepter 1 ex too. Helmet is around 50 chaos and the Anoint requires a golden oil around 40 chaos.
Watchers Eye with Vitality inc life recovery is around 50c depending on other rolls but it's not required. BIS would be that roll and also Phys damage taken as Fire while affected by Purity of Fire but that can cost like 5 ex and maybe impossible to find.

You go walking around with RF and high move speed insta killing packs. Use Infernal Cry to detonate big packs or rares. Periodically casting Storm Brand to proc Elemental Overload and Elemental Equilibrium on tougher mobs. Vaal RF for bosses.
Against bosses you can place your Decoy Totem if you feel you need the extra tankiness and damage it provides.
Keep your immortal call on your left click so it auto casts as you move and you get the most uptime of both the defense it provides and the damage through the expense of your endurance charges while keeping it simple.
Remember to always cast on cooldown Infernal Cry to generate the endurance charges through the Ascendancy passive.
If you get a huge damage spike or no regen for a few seconds like Maven or Sirus beams, turn RF off with dousing flask and life recovers in less than a second thanks to Arakaali power, the turn it again or just channel Scorching Ray.
For no regen maps, swap one flask with enduring mana flask and don't turn normal RF. Just use Scorching Ray and Vaal RF, it will be much slower but still doable.