This map voting addon supports ZS | Zombie survival, ZE | Zombie Escape, TTT | Trouble in Terrorist Town
Install the addon to the "/garrysmod/addons/"
folder.
The path layout should look like this : "/garrysmod/addons/gmod-mapvote/lua/autorun/server/sv_mapvote.lua"
To configure the script to function the way you want edit the following file : https://github.com/C0nw0nk/gmod-mapvote/blob/master/lua/autorun/server/sv_mapvote.lua#L3
Specify the map cycles timers etc
Information available on facepunch thread: http://facepunch.com/showthread.php?t=1268353