[Kwarde]

Uhh it takes quite some time yes. Creating the basics takes some time, and then to implent all the functions you want can take months (if you want a gamemode like Raven's Roleplay, it may take over a year. Also depends on how many time you have). And creating the maps can take some time, if you want stable maps aswell. And then I didn't even mention the errors/warnings you can create in your gamemode while compiling, or even the bugs you can (or mostly will) stumble across to ingame. (I never made a script that worked perfect the first time I ran it).
If I'd start now with that gamemode, I would not be finished within a month. It might be possible, but then you shouldn't expect too much from that gamemode/server.