Now this is pretty cool, I've been working on one myself, though its slow progress as i work 2 other jobs right now. I've got the model done. main thing I've been trying to figure out is how to power the xbox without the psu inside.
check this guys YouTube video, I've been designing my custom slim console off of it with tons of modification to it. May be a fast starting point for the case portion.
files are in his description.