Life Based Righteous Fire is Possible!

Tree
Passive skill tree build

Life regen from tree: 8,4%
Life regen from lvl17 vitality + 31% aura boost from tree: 1,965%
Fire res from lvl20 purity of fire + 31% aura boost: 5%

Fire res from tree + phoenix + pof: 90%

Life degen from RF with these stats: (90*1.03*0.10)-(8.4+1.965)= -1.09%
You regen 1.09% hp

The only "hard" part is getting purity of fire to lvl20, the easiest way to do this is a level 17 pof in a weapon with +1 to gems +2 to fire gems.

Life based Rf builds have been a possibility since the beginning, they haven't been that common because going low life and high ES was by far the better option, that changed upon open release.

The only required unique is rise of the phoenix, degen from ES can be negated due to the shield itself having 6hp regen/s and we regen some % ourselves

From this base you can go the way you want, get evasion, armour, both, IR+US, EB, etc...I guess going for life and aura boost would be a good option, EE + shock is also possible might be even better