Seems pretty basic to me, but since not everyone is like me

The bottom 2 rows are must-haves. [Streamline] for the MUCH needed reduced energy cost. With that, you will be able to sustain your [Arquebex] mode for much longer, as well as cast your storm shroud a lot more. Be sure to cast 2 before 4 though, because you cannot cast abilities in guard mode. That would be too strong IMO.
[Rage] and Repair for the only source of healing a [Voidrig] can get solo, as well as a source of energy that isn't Wellspring. [Flow] to just increase the amount of total nuking time you have.

[Vitality] and [Steel Fiber] for very obvious reasons. It gives you more HP, and more armor which gives you a buttload more EHP (Effective Health points)

Im a tiny bit iffy about [Continuity], since it doesn't add a visible difference to either storm shroud or the energy drain from guard mode. here on overframe. Feel free to go test it, but to be safe, I will keep it here as there is barely anything else that is very useful for a necramech.

The last row, as well as slipstream, are just flex slots (in a way). They can be equally changed to your playstyle,, depending on what you like, of course, but for the sake of a full build.

I like to go fast, so i equip slipstream, thrusters, and friction. This allows for a really long and fast dash time, as well as either longer running speed or a longer hover for [Aviator]. Hydraulics for.. obvious reasons. Higher jump to get to higher places, and also even more time for [Aviator] if you decide to run it. and Augur is truly a flex slot. You really dont have to run this if you dont want to, you can run whatever you want. However, this may either require another forma for whatever costs the most, or just compensating with another one of your flex slots.

You could also run Efficiency for even more engine run time, but that might be a bit overkill on the engine. And [Redirection] will GUARENTEED cost you another forma, so if you want to not waste any forma's, this is (hopefully) the build to go for.

Aviator is something to consider, as 40% is 40%, especially in damage reduction.

Hope you enjoy this! =3

-i love peppersbaybish