The heading should be a memo heading with To: From: Subject: and Date: lines.
The introduction should explain the purpose of the document, the historical context it is addressing, and it should preview the contents of the document. As you discuss the historical context, you will talk about the agreement you think you have reached with your client.
Having divided your project into stages, the first part of the body should describe what you will do in stage one and what the target date for completion is.
Specify the work to be done and the deadlines to be met.
Continue the pattern begun in stages one and two until you have described the whole project.
In the conclusion, draw all of the stages together with their dates in a single table so that the reader can easily see the whole project. End with a confident and reassuring statement.