www.deadm.com

i found a thing online that lets u create ur own maps the only thing is i dont know how to put them on, i think if ur an admin u can put them on urself or u can go online to some web site and do it. any way it is called "Valve Hammer Editor"
like i said i know almost nothing about it but if u like it or find out more plz respond

You use the hammer editor to create the map. You then compile the map using, "Zoner's Half Life Tools". The result of the compile is a .bsp file. You can then copy the .bsp file into the maps directory of a server to play the map.

If you make custom textures you need a .wad editor. It will combine custom textures into a .wad file that you copy into the cstrike directory of the server.

That is the 40,000 foot view of map making. The web is full of tutorials on exactly how to do it all.