Has the grid in the waste of your vanity basin deteriorated and can you not find a replacement one to buy?
Well how about printing your own one using ABS plastic. ABS is widely used in plumbing for things like shower wall linings and this same material happens to be a material many 3D printers print with.
If you still want your own design, then read on?
Step 1: Want to Make Your Own Design
If you are comfortable with programming then I recommend OpenSCAD as you can specify the measurements precisely and create a perfect fit. I have done this for both a Dorf basin and a Caroma basin.
How about making ones with writing, they are unique even if not always very practical. You might get you a kiss or punch from a loved one:-)
So waste your time and create a special message in the sink for someone that needs it.