Creating a RAT is sort of difficult, especially when you want to spread it it.
Go to the hack forums, and choose a free RAT program like DarkComet and search over there. This forum is for SA-MP hacks rather than general ones.
Things you'll need to do it to set one up, create a stub correctly.
Port forward.
Setting up a no-ip DNS server.
Disabling any anti-virus or firewalls that may block Darkcomet incoming connections.
Spreading it, crypting it and all that jazz.
Then you might get a few slaves, there's a ton of TRUSTED services on hackforums that set it up for you for a price. Hey, I hope these mods don't go ape shit but here's a link to the board.
http://hackforums.net/forumdisplay.php?fid=114
Someone has to click your rat for you to get control of their PC, by the way.