A little about the costume first. I have read that Carrie Fisher said that her costumes in the first 2 Star Wars movies were so long that people couldn’t tell if she was a woman. Well, the scanty outfit she wore in Return of the Jedi changed that. The Leia bikini was created by Aggie Guerard Rodgers. The costume department made a mold of Carrie Fisher's body so they could do a custom fit and they made forms of the slave bikini to suit different scenes in the movie. One was a hard metal one that she wore when she was not undertaking any stunts and one was made of formed rubber and lined with leather so it would be a bit more comfortable when doing stunts.
Anyway – How to make a Star Wars Princess Leia Metal Bikini
Put on your favourite cute bra then wrap your chest and shoulders in plastic wrap but not tight so it doesn’t flatten your chest, then use cotton cloth strips and watered down PVA glue as a cloth version of papier mache – I guess cloth mache. Get someone to help you as you can’t glue and stand still at the same time. Work fast as it dries fairly quickly.
When it goes hard you'll have a realistic cast of your breasts and chest area. Use a marker pen to make lines where you will build up on the bra with paper clay (you can get it at art shops - it's like a premade papier mache like soft clay) to mould up the raised metal patterns on the bra. Once it's all dry take it off and seal it all over with PVA then paint in metallic paint etc so it looks the part.
The bottom plate you make the same way and then finish it off by sticking two long strips of red, stretchy fabric to it. The strips should be wide enough to cover the insides of the thighs, about 250mm wide The strips should hang from the front and back of the bikini bottom down to the floor. Straps to hold it all together can be made from leather.
For the headpiece, once again, mold one using paper clay on a piece of cardboard.