Custom games Recreation

I remember back in the good old days when EVERYONE could download games and custom maps in Halo 3 with such game types as Jenga, Infected and all the other awesome maps and modes there was.As a veteran Halo Player I think I am right when i state that those days were the most awesome days of playing halo, therefore I am really REALLY exited about making them all over again.The only problem is? I have absolutley NO idea on how to make the maps nor game modes, so I am wondering if there is ANYONE who would help me in recreating or show me how to make these modes and maps so that I can start delivering these to all my Halo friends. Anyone who can help?