Well, I believe the major Garry's Mod update made all the fretta gamemodes broken and require a fixin' (excluding TTT).
The best way to approach making a map for this would be to decompile the original map and annotate all of the custom entities at work. Here is a
link to the old svn. I think the way GameMaster works is that there are 3-5 rounds each taking place in a separate part of the map. All of the other components are self-explanatory and the one major thing to keep in mind is how the map should be oriented and how far it is from the origin so the players are looking at the correct angle AND that the background is composed of a grid.
Then again, testing the map will require a working version... and if there is one, good luck.
