It would help to know what your experience is, and why they put this task in your hands. Do you work for a mold builder or Molder? What is your familiarity with molds?
There are some quoting softwares out there, but they aren't neccessary, and don't account for a lot of variables.
Evidently, unless your employer isn't very sharp, they think you have the experience to do this.
I'd start collecting mold base and component catalogs & steel suppliers catalogs, and talk to your shop floor and see what is involved with building different types of molds.
David