Hey, I've been days trying to figure out how to add custom maps to the mani menu inside CS:S.
I recently found this forum and found that similar problems where on this thread so I'd thought I'd post.
Any suggestions would be a massive help -
Gregorah

Add the map name to votemaplist.txt, maplist.txt, and mapcycle.txt if you want them to be on the rotation.

They should be in your /addon/cstrike folder.

You will have to restart your server in order for the changes to take effect.