Step 1: Materials
I ended up using almost a yard of lycra and half a yard of the power net (a stretchy mesh). This was mostly because I was experimenting a lot. Once you have your pattern made, you should easily be able to determine how much material you need.
I opted for two bottle openers, which I got from Amazon.com.
I also used swimsuit elastic for the bottoms (won't break down in chlorine), and clear elastic for the top, and a hook for the back.
You can also add modesty cups for the top, or underwires, or even padded cups. I tried this out, and decided not to use them.
Step 2: Pattern
Decide on what shape you want your beerkini to be. I'm sure this would also work as a one-piece with an inset bottle opener too!
I used a couple swimsuits I already had to draft some patterns, chose one, and tweaked it from there. I am fortunate to have a dressform that is approximately my size to pin things to and fuss with the shapes. My next version would definitely have a more modest bottom. I'm really not sure I would wear this in public.
I've attached the pattern I used for you to use, tweak, or modify as you see fit.
Step 3: Cut pieces
Make sure you align the lycra to one long edge of a table before you cut it so it's not all twisted and warped. Place your pattern pieces on the fabric and use weights to hold them in place. Pinning the pieces may lead to runs in the fabric.
Trace along the outside of the pattern with chalk, and then again about 3/8" or 1/2" outside of the line for seam allowance.
Cut along the outside line you've marked.