Decision Tree for SQL Server Consolidation

Hi,

I have been asked to Design a Decision Tree for the consolidation of SQL Server 2005 to SQL Server 2008 which might involve the moving the instances to the new hardware in another place( data center).

What are the steps I need to take into consideration to achieve this. I have been asked to design it using some graphical represent like visio etc. The next steps depend on this and I need to do this ASAP.

Thanks in advance,