No sure what you mean by 'create'. If you mean you are using a standard library part window and want an asymmetric grid, I don't believe that is possible with the USA library that I have... not sure if there is a special window in the INT library. I think Cadimage has editable hotspots on the divider bars that let you position them where you want them.
If you mean 'create' from scratch and save as a custom window, then the easiest is to model a custom glazing panel and reference that in the window library part that you want to use. As you scroll down the images of grid options you'll see Custom where you can reference a custom window panel that you save in your (embedded) library.
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