Currently involved with an assignment which needs me to create a 'mock concept art brief' from a fictitious production company.

Now the questions...
Is there any format to adhere to with regards to professional briefs, or can it greatly vary from job to job?

If a company hired an artist (or group) to create the entire design portfolio for a project would they list the items needed (i.e. 3 vehicles/4 main characters/ 7 environments etc) or simply say 'Create a world in the style of 'X' ... ?

I have a funny feeling that I may already know the answer to this however its best to ask those who have been there done that, just to check.

Appreciate any information,
All the best...

-Cuervo