in reply to module needs another module for build

build_requires will be resolved too late to be of any help. build_requires are resolved by *after* Makefile.PL has already been executed by cpan/cpanp/cpanm etc.

CONFIGURE_REQUIRES on the other hand are a list of prereqs that must be resolved *before* Makefile.PL is executed.

WriteMakefile( CONFIGURE_REQUIRES => { 'B' => 0, }, PREREQ_PM => { 'B' => 0, }, )

We require the 'B' module during configuration and at runtime in the above example.