Question

I just want to know what do I need to write in the Makefile.am to create a directory called build in the same directory where Makefile.am is.

Answer 1

You would need to write:

build:
    test -d ${srcdir}/build || mkdir ${srcdir}/build

but you really do not want to do that. The source directory should be considered read-only. If you simply want to create a directory named build in the build directory, just do

build:    
    test -d build || mkdir build