I made my Barbie box out of Sonic Drive-In cup boxes that I got from the store manager for my Homemade Barbie in a Box Halloween Costume. Their boxes are long and narrow, unlike normal storage boxes. I used two that I slid into one another and taped down. I put a cord through the back around the height of my hips and tied the cord around my waist to help support the box. I only had to hold it up a little with my hands.
I used wrapping paper and used stick glued it down. I printed Barbie logos off the internet and blew them up and cut and pasted them on the box. I actually got my dress from a prom store on sale. I decided to get a curly wig instead of straight to make it a little more interesting. I also wore big fake eye lashes and glittery shadow. The plastic is saran wrap I straightened out and it is removable if you use normal scotch tape. I would even suggest just not having it because it got really hot in there and it looked just as good with out it.