Making a concrete sink is easy, and fairly inexpensive. Most of the materials for making the mold can be found as scrap pieces from old furniture. This project can be done under 100$, and is worth every dollar because it will make you feel REALLY good about yourself every time you use it.
Step 1: Taking Mesurements
First I removed everything from atop your old sink countertop, along with faucets and drain stopper. Then I used some tracing paper, and, Indiana Jones style, rubbed the outlines of all the holes. After doing this, I "expanded" the holes by just a hair (1/16th on an inch) on my drawing, to make sure that everything fits into the holes (yet still get covered up by the hardware removed), and i wouldn't have to do any concrete grinding after it's all poured. Many sources like CHENG Concrete and Expressions-LTD sell rubber plugs to me these holes even more effortlessly.
I then cut out all of the holes from my template and cut up some wood to make the mold. It is recommended that you use smooth surfaced material to make your mold, mine had a little texture in it to help me replicate a wood finish on my final product. I then sealed the corners with some caulk. The height of my new countertop was 2" as recommended as the minimum on the concrete I used. I had then traced all other markings from my template to the bottom of the wood, so I could add my mold forms for all my holes.
(I was making two sink countertops, in case I didn't like the first one, that's why there are two molds)