Writing Build scripts for multiple nested directories

(Originally posted <a
href="http://groups.google.com/group/comp.lang.perl.modules/browse_frm/thread/0b65273ac4c98046">here</a>
but was referred to this group)
---
Basically I am kinda confused about the structure and packaging for
different modules that I am trying to build.  Do I need different
Build.PL files for each folder and a different package and whatnot?
And after I get that whole mess taken care of, how do I go about having
the build process automatically build missing modules?

HC
  | A.pm, M.pm
  |-- A
       | I.pm, D.pm
       |-- I
       |-- D
            | IE.pm, MO.pm
            |-- IE
            |-- MO
  |-- M
       | FW.pm, VM.pm
       |--FW
       |--VM