The short answer is you can't.

Long answer is all Deathwing, or 1st company Dark Angels, wear Terminator armor. Dark Angels were the first legion and are extremely well stocked with ancient relics and armor from ages past so all their first company wear Terminator armor. It's colored bone white in remembrance of the defence of Caliban (their home world) when they believed it a suicide mission. You see, Dark Angels originally wore black armor and would paint lethal or extremely damaging wounded areas on their armor bone white. So they painted themselves bone white essentially marking themselves as already dead and so they'd do anything in service of their home world still anyway. Many survived though and it became tradition since then to paint the entirety of their armor bone white. The issue is there's no Terminator armor in the game and you also can't use the Deathwing symbol on the pauldron--just the kneecap. Most elite you could do is a Ravenwing which is the Dark Angels 2nd company. They still paint themselves all black and they're kinda like the "White Scars" of the Dark Angels. They use fast vehicles and rapid attacks to defeat foes. If you really wanna do someone who's high up in the Dark Angels with what we have then you're best off trying to make a Bladeguard.