Brand guidelines from existing logo

We need a set of guidelines outlining how to use our existing logo and which colours should be our main colours.

We need to define the ways that the logo can be used and the various forms it can take- e.g. whited out/ all black/ one colour/ two colour. Need to show the clearance around it and which logo is appropriate for each circumstance.

We know what the guidelines should be but not to phrase them and how to create a brand guideline document suitable for sending to designers and agencies. We are a registered charity.