So let's say that you make a pepakura marine suit and you have an accurate set of clothing underneath the armor. Once the armor was resined and painted, it should technically be considered screen accurate, right? I mean, it is an exact replica from the game, the same idea as taking a suit of stormtrooper armor and copying it.
On a side note, we should get a section of the site set to tutorials. This site has help, but if we had all the knowledge you would need in one place, it'd make things a lot easier.
(for example)
halo 1 marine armor
1. Fabric for undersuit (what kind to get, what colors to look for)
2. Sculpting your armor (pepakura models, vacu-forming tutorial, etc.)
3. Making your helmet (lining the inside, eyepiece, etc.)
3. Detailing your armor (what colors to use, how to weather, etc.)
4. Putting it all together (attaching the armor, making it comfortable, etc.)
Hope this helps