select arch with debuild

i converted sourcecode with dh_make , modified makefile and debian/* and succesfully compiled and buid package with debuild but can't select arch. in fact debuild (at some lines) says: make[2]: Entering directory `/home/pelux/temp/mplayer-0.11.pre24/libmpeg2' gcc -c -O4 -march=i686 -mcpu=i686 -pi

help dh_make + debuild (with orig source code) !

I get with every package an error compiling with debuild a debianazied regular source package converted with dh_make in fact (this is mplayer 0.11pre24) debuild says: dh_installdirs # Add here commands to install the package into debian/mplayer. make install prefix=/tmp/mplayer-0.11/debian/mplay