Network needs analysis template

I have a client that requires a comprehensive needs analysis executed on their exisiting infrastructure. With so many variables and strategies it seems difficult to complete this in a comprehensive manner. With this in mind I am looking for advise and / or templates on how to complete this with the least amount o inconvenience to the client while making sure that the questions that need to answered are leaving a minimal margin for error.

I appreciate that a comprehensive analysis of the clients existing infrastructure, systems and proceedures must take place and I am wondering if anyone has a set of templates, checklists etc that can assist in achieving this.

If such a series of documents doesn't exist we should put them together as a group. What a valuable tool set that would be!