Here's the Cortana journal, where I'll post information and progress shots for the process of making my Cortana cosplay. For this specific costume I think I'll be posting as little photos as I can, due to its simplicity. But many pictures will be taken of the final result.

Materials Needed:
Zentai SuitAirbrushing
Face/Body Paint
Hair Spray
Blue Flats
Warning, long read ahead.
04.06.11 The suit was actually not fitted very well (thats what happens when someone does it for free yes?), and thanks to the marvelous person whos going to paint the suit, their marvelous wife will fit it properly. Were still working out what days to meet on, but sooner than later the costume will be fitted and then painted and then complete minus the correct hair spray color and face paint.
For face paint Im looking into airbrushing, but Im worried that the mechanism for that will cost an awful lot.

Ill learn when I go hunting for it. If so Ill just stay happy with cake makeup. Im told it can crack, but I think with the right planning Ill be able to avoid that entirely or keep an eye out and fix it up at the conventions throughout the day.
As for shoes, I cant find the proper color in the slightest. So once the body suit is completed, if Im still not able to find shoes, I will buy a pair of white flats, either faux-leather looking or faux-suede looking and spray paint them the color I need. Ive learned that spray paint is not only affordable, but also comes in a much greater array of colors than I originally thought (and its super fun to use! ^^).
10.22.10 I've been talking about doing a Cortana costume since I first realized how fun cosplaying was [around 2008]. After much fiddling around on the internet and failing several times getting a commissioner, I stumbled across zentai suits. These seemed to be the perfect, and I searched through several sites looking for the perfect color.
I happened to find one over a year ago. Then through my schedule going crazy I was unable to purchase one right away, and after a few months I put the costume on hold, for no real reason it seemed.
About a month ago I decided to pick it back up, probably due to my hype around wanting to do a Big Daddy, splicer, and Little Sister cosplay with Ron and my sister. I went back to the site I originally found the zentai suit with the right color, only to find they no longer sold that color. After plenty of cussing I went back to the internet drawing board to find another zentai suit.
Lo and behold, I happened upon one. On a site that sold them for very cheap, custom sized, hoodless, seamless, and in the perfect color. It took a few weeks before I could buy the suit, but finally I ordered it and waited patiently for it to come in the mail.
A year ago when I was determined to get my Cortana cosplay finished as soon as possible,I found a very nice, and relatively local, airbrush artist willing to paint the light blue suit with the proper pattern to resemble Cortana's. Thankfully he is still on DA and is still willing to paint the costume, and on a future date we will do so.
Towards the end of September I received the suit, but it was not the advertised color. I was disappointed, but it was still a shade of blue that could be used as Cortana. Then when I tried it on for the first time, it hardly fit properly. I stretched where it should have hugged mostly. Skip forward a few weeks and today I'll be picking up the fitted costume, ready for painting.
My biggest concern now is finding the proper color to spray my hair, as it needs to match the color of the darker blue design on Cortana's body. But I won't know how big an issue this will be until the costume is airbrushed. I am less concerned about finding face paint, as the blue of the suit seems easy to color match.
The next issue is to protect the soles of the feet on the costume. The material can snag easily, and can get dirtied very quickly on the ground. So I am in the process of finding matching blue shoes, preferably flats to minimize how much of the costume the shoes will cover up, as well as make it extremely simple to slip them off when needed.