I always find it helpful to draw a little sketch, and what comes next is some simple math.
Just think: what is your dx and dy, and how many grid points with that size (dx, dy) do you need to get from the center of your domain to the boundaries, covering the area of interest? That's your e_we/e_sn.
Run geogrid/ungrib/metgrid and take a look at your domain.
Adjust the domain setup if necessary.