Hey, I can't really understand the question you are asking. Are you talking about using mega blocks to scale for a pepakura build; if you could explain your question a bit better that'd be great.
You can certainly scale down files to that size - but you're going to have a very, very tough time of assembling them. A lot of the files we host here are designed for full-scale costumes rather than for producing miniature figurine pieces.
There are files for vehicles. I know there is at least a scorpion, warthog and ghost. However, building it at that small of a scale will be really tough since there are very small pieces. I don't understand why you would want to build something that small out of cardstock. Wouldn't it just be easier to get the Halo mega blok sets and biuld it that way? There are no buildings that I know of. Here, on this site, modelers mainly create files that we can use to create costumes to wear, not really anything of what you are looking for. If you are looking for smaller things, you may want to search around for paper craft sites.