I have been playing around with drafting my own bra patterns from scratch. This necessitates a lot of testing. I was finding it hard to assess the fit of the cups without making the complete bra, which was time consuming. I also didn't want to deplete all my bra-making supplies. This is my new approach:
Cut out the cup pieces and the bra cradle in a woven fabric. Stitch the cups pieces together and then stitch the completed cups into the cradle.
Then I stitch down the seam allowance between the cups and the cradle. The seam allowance is only 6 mm wide. I can stitch the seam allowances down to form a channel that is 3 - 4 mm wide. This is wide enough to slip in the bra wires, without having to sew on a separate wire casing.
I can then use one hand to hold the wire beneath my breast and the other can hold the strap position. The wire helps hold the cups to my body and I can get a good idea of fit. It only takes about 10 minutes to cut out and sew up and I have used precious few materials.