I question I need Answered
 

I have seen singleplayer maps built by people which are really cool...but is there a way to where you can make a singplayer map that you can play with a friend like a co-op mode? Ok thanks!

--Zach

Yeah there is a way i think some people did it before

start your own server.
make sure he is also in it
type "maplist" (no quotes) in console
double click your desired map.
have fun

some maps it doesnt work but some it does. make sure to move right away when you spawn cause your buddy should spawn next and if you interspawn you will die.