With a mock building tool can greatly reduce the planning time and get a clear picture of what information will be needed on each page.
Here are a few of them:
Pencil - free and opensource tool for making diagrams and GUI prototyping http://pencil.evolus.vn/en-US/Home.aspx
Mockup Builder - http://mockupbuilder.com/
Cacoo - http://cacoo.com/
MockFlow - http://www.mockflow.com/
LucidChart - http://www.lucidchart.com/
HotGloo - http://www.hotgloo.com/