im making a serveratings plugin here is what i have so far

PHP:

<?php

/*
__PocketMine Plugin__
name=Server Rating
description=tells console the player's rating about the server
version=1.0
author=jerlegoman
class=rating
apiversion=10,11
*/

/*
Descrption:
Have you ever wondered what guests on your server think of your server? well now you can with the server rating plugin. this plugin uses 4 commands for different ratings. The plugin has rate bad, rate ok, rate good and rate great.
To get the most out of this plugin use the Signconsole plugin and the EchoCommand plugin then all the person has to do is click on the sign and it sends the rating to the console and if you use the EchoCommand plugin you can see who sent the rating.
================
Commands :
/ratebad - gives bad rating
/rateok - gives an ok rating
/rategood - gives rating good
/rategreat - gives rating great
*/

/*
Change logs

1.0
doesnt save ratings yet

*/

class rating implements Plugin{
  private $api;

  public function __construct(ServerAPI $api, $server = false){
    $this->api = $api;
  }

  public function init(){
    $this->api->console->register("ratebad","send to console bad", array($this, "serverbad"));
    $this->api->console->register("rateok","send to console ok", array($this, "serverok"));
    $this->api->console->register("rategood","send to console good", array($this, "servergood"));
    $this->api->console->register("rategreat","send to console great", array($this, "servergreat"));
  }

  public function serverbad($cmd, $args){
    $this->api->console->run("tell console server is bad");
  }
 
  public function serverok($cmd, $args){
    $this->api->console->run("tell console server is ok");
  }
 
  public function servergood($cmd, $args){
          $this->api->console->run("tell console server is good");
  }

      public function servergreat($cmd, $args){
          $this->api->console->run("tell console server is great");
  }
 
  public function __destruct(){
  }
}
?>

It works but maybe someone can help me make it better

First of all don't do /tell console
Do console() instead.

Second, the best method to save is

PHP:

if(in_array($rater->username,explode("\n",file_get_contents($theFilePathWhereYouSaveThePlayers))))return "You already rated";
file_put_contents($rater->username,FILE_APPEND);
file_put_contents(file_get_contents($fileWhereYouSaveANumberThatIsTheSumOfRatings)+$rating);

For $rating, it should range from -2 to 2, excluding 0 (which means I give up the right to vote)

is there a way to save it to a config

There is of course, but since you are saving strings and numbers only, it is higher efficiency to save it in plain text.
I was in a hurry last night, and this is the better code:

PHP:

class Serveratings implements Plugin{
private $dir=ServerAPI::request()->api->plugin->configPath($this);
private $cmds=array("rategreat","rategood","rateng","ratepoor","raterubbish");//rateng is rate-no-good
public function __construct(ServerAPI $api,$s=0){}
public function __destruct(){}
public function init(){
  foreach($this->cmds as $cmd){
    ServerAPI::request()->api->console->register($cmd,"rate the server",array($this,"cmdHandler"));
  }
}
public function cmdHandler($cmd,$arg,$rater){
  switchw($cmd){
    case $this->cmds[0]:
      return $this->rate(2,$rater);
    case $this->cmds[1]:
      return $this->rate(1,$rater);
    case $this->cmds[2]:
      return $this->rate(-1,$rater);
    case $this->cmds[3]:
      return $this->rate(-2,$rater);
    case $this->cmds[4]:
      return $this->rate(-3,$rater);
  }
}
private function rate($score,$rater){
  $data=explode("\n",file_get_contents($this->dir."Raters.txt"));
  if($data!==false and in_array($rater->username,$data))
    return "You cannot rate twice.";
  file_put_contents($this->dir."Raters.txt","\n".$rater->username,FILE_APPEND);
  $rating=file_get_contents($this->dir."SumedRate.txt");
  $rate=($rating===false?0:(int)$rating)+score;
  file_put_contents($this->dir."Raters.txt",$rate);
}

Well basically I made the whole plugin for you.
To give you a chance to make your own plugin, you can improve the file functions using this:
http://hk2.php.net/manual/en/ref.filesystem.php
note the fopen(), fwrite(), fread() and fclose() functions.