How do I make this?

     Ok, I use solid works to create parts and sometimes mate them together.  Now I need to design a steel rack for the shop and need to kind of create it as I go.  It will not work for me to make each part in a separate file and then mate.  I need to envision it as I go.  So how do I do this?  I want to have a BOM when I am done.  Should I start out in assembly?

SolidworksAssemblies