Precious little I'm afraid, though this is unfortunate. I've seen a Master Chief scratchbuild/sculpt once. And somewhere on the HBO (halosm.bungie.org, not the cable network) one of the guys who has done substantial analysis of the game maps vs. the actual objects, e.g. that a large fraction of the combat done by the Master Chief when 'on' the Pillar of Autumn actually takes place outside of the 'Pillar, started a massive Pillar of Autumn scratchbuild, but at least on the website, was never completed.
I, myself, have a strong desire in scratchbuilding a Warthog & Pelican in the same scale but I've since found some schematics that indicates that a Pelican is a fairly large aircraft (drop ship?), and even in 1/72 has something like a 24" wing span. I have occasionally thought about just scratchbuilding a 1/35 scale Warthog, but this was put on the back burner compared to some other projects. And if I can find some decent orthogonal renders, I'd love to build a Covenant Phantom, but as is usually the case with these things, about the time I find decent reference material, the subject has become 'moribund.'