Question about creating web standards for a corporate intranet

If you had to create a manual describing the web standards for a large organization’s intranet,
how would you go about creating it?

What would be the purpose for an intranet standards manual?

Have you been asked to do one? If so, what was the rationale for it? Do employees need to be educated about certain things? There is no rule for what to put in a manual. You can be guided by what purpose the manual needs to fulfil.