well heres a bit of a selection that I find appear like the suits would be like just with about the height of 8-10 feet.

http://img1.wikia.nocookie.net/__cb20130714105253/redfaction/images/d/dd/Leo_exo_suit.jpg

http://fc05.deviantart.net/fs7/i/2005/209/8/a/Exo_suit_by_flyingdebris.jpg

http://th07.deviantart.net/fs71/PRE/i/2013/344/5/2/heavy_exosuit_by_km33-d6xfoqo.jpg (this one may be a good fit for the marine.)

http://digital-art-gallery.com/oid/105/640x905_18286_Peregrinus_III_2d_sci_fi_character_exosuit_picture_image_digital_art.jpg (this one is a bit heavier, so maybe it'd work for either the marine or the engineer[which is already taken so whatever])

http://www.neomagination.com/dominance/Starcraft/Marine/Render_01.jpg

http://www.issahcontractor.com/images/indie_gogo/armor.jpg (although this one is heavily armed it's a good size comparison for the light end of exo suits, so it'd be more like a scout.)