How to make dimension for CNC Router

If you're asking about the maximum dimensions/limits of a CNC router, it depends on which machine you're using. Some routers are larger than others.

One limiting factor is what you plan to cut in the router. If standard sheet product is available in 4' x 8' sheets, then it does not make sense to make the router larger than that.
How big is the material you intend to put in the router?

we work with a 60" x 120" cnc

Yes possible, but inside of the maximum work area...