Hej,
Well I made a chainmail bra recently, and I decided to share my experience here. Enjoy.
On that model, I used 1.8mm wire and 8mm rings. I also made one with 10mm rings before that one.
Making rings :
You will easily find plenty of sites explaining that. In order to give
the ring shape to your wire, you will roll it around something which
is cylinder shaped, and which has the diameter you want for your rings.
You get something like that :
Once you have that "spring", you will just cut each ring off it.
Making european 4 in 1 chainmail :
Again, there are many sites explaining how to make 4 in 1 standard
european chainmail. It doesn't require much skills. The main skill you
will need is patience in my opinion. Luckily you won't need to put
together 15k rings for a bra, unless you want it to fit non-human
breasts.
Starting the cups :
Here is the key of your bra. You will have to make a "45° seam".
Why ? That will create the volume of your cups, together with the next
step, which will tighten the base part of the cups.
You start with a triangle like this :
Then another, a copy of the first one :
Place them that way : (The
colored spots show the 4 rings your ring will pass through). Click on the picture to enlarge.
It's extremely important how you place them, because once it's well
placed, it just seems logical how you have to add the rings. Click on the picture to enlarge.
From now it's just obvious how to continue the 45° seam. Here is the result :

That will be the upper part of the cup.