Chosing the right fabricator:
Will your installer weld/solder the seams?
Welded seams, as we'll touch on later, are very important to the longevity of your countertop. If your contractor is not goning to be welding/soldering your seams, it's likely that water will get under the zinc sheets and damage the wood under it.
How is your fabricator getting their measurements for the new countertop?
Long distance manufacturers will most likely make a perfectly square template: once it's shipped to you, it won't run flush with the wall. We measure on site and make the template to fit EXACTLY.
Will your installer check the measurements with any preceeding cabinets or plumbing?
Zinc countertops are very hard to alter. If you're going to have plumbing or electrical work done around your new zinc countertop it's very important that your contractor knows and can work with your countertop fabricator!