Inaros Prime is a great Warframe to play right now. With the introduction of The Steel Path, survival has become more important than ever. Inaros Prime lets you create a Forma Zero version that will passively sustain, allowing you to focus on the act of destroying your enemies.
The main issue people face when building Inaros Prime is wishing it was something it isn't. This is in part due to his popularity, where people don't want to admit he's an extremely easy Warframe to play, as he rarely dies. Rhino will often be seen as a noob friendly Warframe, but people don't want to extend that same title to Inaros. The best builds for this frame are based on what it does best, which is absorbing damage.
Stacking the three Umbral mods of Vitality, Intensity and Fiber will give him a lot of health, armor and potency, and we can use Gladiator Resolve and Gladiator Aegis to increase health and armor even more. Adaptation will reduce incoming damage, and Rage will keep us constantly energized, allowing us to spam Desiccation, blinding enemies and stealing their health.
Where the above build will get a bit tricky for some players are the full stacks of Arcane Grace, which will heal us ad infinitum depending on incoming damage, and Arcane Guardian which will give us massive armor gain. under the same circumstances.
The Aura slot can be used for corrosive projection to reduce enemy armor, or steel charge, increasing melee damage. In the Exilus slot, I like to put Rush on almost every Warframe, just because the speed is nice.
This version will provide incredible passive healing and tanking, and you can even add a Forma if you want to include a mode like Stretch for more scope on Desiccation, or Negation Swarm to reduce incoming status effects and knockdowns.