Below is invocation to create an OS X Yosemite USB Installer in the Terminal.
Invocation
sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia –volume /Volumes/Yosemite –applicationpath /Applications/Install\ OS\ X\ Yosemite.appResults
Ready to start.To continue we need to erase the disk at /Volumes/Yosemite.
If you wish to continue type (Y) then press return: Y
Erasing Disk: 0%… 10%… 20%… 30%…100%…
Copying installer files to disk…
Copy complete.
Making disk bootable…
Copying boot files…
Copy complete.
Done.