This is Garrus Helmet of Terminus Assault armor set from Mass Effect 2.
The Terminus Weapon and Armor is a DLC (downloadable content) pack which is given to those who pre-order ME 2.
It’s also available on Mass Effect 3.
The dlc ads 10% increase sprint, 10% reserve ammo and +15% shield. The bonus effect is different in ME 3 and in ME 3 the armor pack is buy-able at Batarian State Arms.
The helm has 129 parts within 11 page, which is quite a lot but the parts are fairly big. Might be easier for you to assemble that way?
It’s a 1:1 scale which means you can wear it and resize it according to your head size. Made by Sinner.