How to do an assessment?
Before taking on any project, especially with a new client, I always insist on doing an assessment. An assessment should be used to uncover any issues that may impact the project (aka. a GAP analysis). Depending on what the project is depends on what you will need, you may need access to switch configurations, file data sizes, logon scripts (if anyone is still using them), and so on.
You will find that the customer will have most of this information readily at hand in different locations. It is my job to interpret the data, ask questions and make recommendations to stakeholders and decision makers. All this data is cleaned up and is usually included as a series of appendices at the end of the assessment document.
The assessment document should be written so that no matter the stakeholder or decision makers background they will comprehend a specific section. The executive sections should highlight benefits of the project, while the technical piece should highlight the design benefits.
If you have competing views of how a project designed, include full work ups of both all designs with costs and associated pros and cons. This will help show everyone which design is better from multiple points of view.
So we know the document has an executive section and a technical section. The document should be wrapped up with a cost analysis section stating the cost of the project, some high-level milestones and deliverables.