Default [Q] Building from source for multiple devices

Just wondering how I can build pacrom for multiple devices, i.e. my nexus 5 and nexus 4

when I run
 ./build-pac -c -s hammerhead
it says
No external out, using default (/home/mk/android/out)
so I'm assuming there is a way to define where you want to output files to. I'm sure it's something easy but I can't seem to figure it out. I want to be able to have both devices building