well,there's a good website called left4deadmaps or somthing,just google that website and it (might) tell you how to add maps.
that helps a lot but i still don't know what ones are most commonly used
Helms Deep looks like an awesome survival maphttp://www.l4dmaps.com/mirrors.php?file=1274also i still don't know how to install the maps properly
Helms Deep is actually really laggy