Hehehe that's my cosplay :P I was GLaDOS last summer, exactly that version !
here's me and my cousin,
What I did was making my own skirt ( WITH PRETTY SHITTY EXPLAINATIONS I GOT ONLINE, BUY A PATTERN, PLEASE ! lol ) with white cotton. You can find some pleated skirts patterns in your fabric store,
Then I bought a white blouse, removed the sleeves and sewn the black ribbons,
for the arm warmers, I found that tutorial : http://hilderic-theknight.deviantart...t=144#/d1kmibh
Hope this helps ! if you have any questions for that cosplay, pm me ! or contact me on my dA !