Run the make file from the root directory of ReactOS. In order to build a bootable ISO image, you must first build freeldr then run "make install" ; next you must run "make bootcd" from the root ReactOS directory. The ISO image will be located in the root ReactOS directory when it is finsihed.
In a reactos/windows build environment mingw32-make must be used instead of make
See the top-level Makefile for documentation on the build targets and environment variables available to configure desired build options.
Please see the platform specific pages for build troublesooting information.