While looking through this site for costume ideas for work (BIG competition at work!) I came across the Lego Guys! They made the BEST Lego Minifigure costumes EVER!! I guess that is why they are your 2009 winners! Well I took their directions and made myself a homemade Girl Lego Minifigure costume!
I used foam core to create the head, legs and sides of the midsection. I took cardboard boxes & duct tape to shape and create the body. I covered the entire costume in poster board and painted the face and hands yellow, and painted the body pink (I work in a breast cancer facility & Oct is breast cancer awareness month!).
I used poster foam to create the hair and face. The mouth is a screen so that I could see out. I took 1st place at my job for best costume. It took about 3 weeks on and off to make and total cost $100.