[Giacomand]

You could do something like this:

pawn Code:

forward rotation(); // The call back Timer.

public OnGameModeInit()

{
SetTimer("rotation", 100, 1); // The timer which will go off every millisecond.
object = CreateObject(modelid, Float:X, Float:Y, Float:Z, Float:rX, Float:rY, Float:rZ); // The object (Fill in the spaces)

}

public rotation() // The callback

{
SetObjectRot(object, 0, 0, +0.1); // Will set the Z rot +0.1 every millisecond
return 1;
}