This was a really small thing to do its got a few bugs like bots dont move and stuff please go easy on this cos its my proper first map that isnt fully mine i give all credit to the maker off phys_cliffhouse Please try it.
INSTALL:put in maps in Left4dead start any l4d campain and then put changelevel:phys_cliffhouse2_d
And it should work :D Oh and if you get Nav error map is unplayble just click ok you can still play it.