Redditor cebt recently showed off his handmade N7 armor inspired by Mass Effect. He used foam for the armor pieces and did an impressive job of giving it a brushed metal look. He spent about three months total on the costume, but that included starting over after he began (he had to scrap some parts) and experimenting with new methods for sealing the foam. He focused on the painting and said:
i actually played around with the color a bit, at first the suit was painted with a gun metal grey plastidip which acted as a sealant and primer, then i rubbed the entire suit with an acrylic color called pearl anthracite, using a sponge.
for the darker parts of the suit i then mixed a batch of black, pearl anthracite and a bit of silver paint.. i really like how it turned out, i do plan on adding some highlights to the suit as well..
i ran out of time before this competition where the picture was taken.