Is the waf 'top' directory the default starting path?

Question

I have a very simple waf script that I'm using to (at the moment) call out to another build system (baby steps you see). Our 'build' folder is under our source folder, so I figured using the first line

top = '..'

would set waf to look for source files starting at that directory for any build commands. However, when running waf, it's not moving to top, it's moving to the build directory

c:\Projects\MyProject\src\build>c:\Python26\python.exe waf
Waf: Entering directory `c:\Projects\MyProject\src\build\waf_build'
Waf: Leaving directory `c:\Projects\MyProject\src\build\waf_build'
input file 'input' could not be found ('c:\\Projects\\MyProject\\src\\build'

Is top not the directory for it to start looking in? Is there a way to set this directory?