[Niixie]

Go in debug, stand the place you want to be a gate and do "/save gateclosed" then you go to the place the gate should go, when its open and do "/save gateopen" then you have the gate, when its open and closed. now you only need to make a command of it.
((Easyer to make gates if you have a map editor))

Read this tut. http://forum.sa-mp.com/index.php?topic=83805.0