Use external storage for roms, RetroPie

Place your roms in external storage using directory structure:

/psx
/nes
/genesis

Do not use like this!:

/roms/psx
/roms/nes
/roms/genesis

Push fresh RetroPie image

Use putty and ssh into the pi.

Install NTFS files system support:

sudo apt-get install ntfs-3g -y

If you are not using putty you have to quit emulation station using menu.
Select quit emulation station. This will jump you into terminal window:

Now you plug your ntfs media and mount with command:

sudo mount -t ntfs-3g -o uid=pi,gid=pi /dev/sda1 /home/pi/RetroPie/roms/

Now you can execute again emulation station with command:

emulationstation

Or you can modify settings so this will work in the next startup automatically.
Open fstab:

sudo nano /etc/fstab

At the end add:

/dev/sda1 /home/pi/RetroPie/roms ntfs-3g 0 1