Install tint2.
$ sudo apt-get install tint2
Edit the config file (~/.config/tint2/tint2rc) to customize.
If you want to enable autohide, add
... # Panel Autohide autohide = 1 ...
to the rc file.
You should also add tint2 to the list of startup programs. See how to run programs during GNOME startup
You should read the full tint2 configuration docs.