Create a Template
The most accurate way to get measurements for your fabricator is to make a template from cardboard, thin luan plywood or even Mylar plastic.
Scribe the template so that it fits snugly against the wall along the entire run of cabinets before tracing the front edge onto the template.
In your template, you must measure the exact locations of cutouts for sinks and cooktops, and holes for faucets and soap dispensers. Be careful not to allow a span of more than 2 feet between cabinets, such as a span over a dishwasher. And allow no more than 6 inches of unsupported overhang with 2-centimeter stone and 9 inches with 3-centimeter stone.
If you plan an undermount sink, make note of that on the template for the fabricator, who will be able to cut a groove along the underside edge of the sink hole, so that the sink clips can be secured.
Also, insist that your fabricator “rod” the cutouts with steel or fiberglass reinforcements to strengthen the narrow areas around the cutouts.
Remember, if you’ll feel more comfortable, you can always negotiate an itemized price for your stone fabricator to come and take the measurements to ensure accuracy.
Once you've clearly specified your requirements and submitted your measurements, set a date for pickup or delivery of your finished countertops.