How to plan a wargaming scenario?

[Joe98]

I am not referring to any specific wargame here, instead I am looking for a generic answer.

In a scenario editor, typically you create a map, set the objectives and give points values to the objectives.

Then you create units and give points values to the units.
Then you create victory levels based on points ( or what ever).

1. Where can I get the imagination from to make a scenario?
2. Is there a mathematical formula I can use to apply points values to units and objectives?