I did a resource justification recently. We, however, did not use a letter.
We took all active and pending projects
- identified the dates they were "required" by the business
- did a project plan with the current resources showing when we could work on then
- did a plan with the proposed resources which showed what we need to meet the business required dates.
- provided a summary of the results and used the more detailed plans to back up the summary.
This took a lot of work but we did get some resources.
I have not failed. I've just found 10,000 ways that won't work" --Thomas Edison