Here is an example makefile (named GNUmakefile to emphasis the fact that it relies on special features of the GNU make program).
#
# An example GNUmakefile
#
# Include the common variables defined by the Makefile Package
include $(GNUSTEP_MAKEFILES)/common.make
# Build a simple Objective-C program
OBJC_PROGRAM_NAME = simple
# The Objective-C files to compile
simple_OBJC_FILES = simple.m
-include GNUmakefile.preamble
# Include in the rules for making Objective-C programs
include $(GNUSTEP_MAKEFILES)/objc.make
-include GNUmakefile.postamble
This is all that is necessary to define the project.