[DJDhan]

At the top

Code:

gPlayerClass[MAX_PLAYERS];

Then create an admin skin like so:

Code:

adminskin = AddPlayerClass(.......................);

Under

Code:

public OnPlayerRequestClass(playerid,classid)
{
  gPlayerClass[playerid]=classid;
}

Code:

public OnPlayerRequestSpawn(playerid)
{
  if(gPlayerClass[playerid] == adminskin && if(PlayerInfo[playerid][pAdmin] < 2)) //use your own variables here for "PlayerInfo...."
  {
    SendClientMessage(playerid,0xff0000aa,"This skin is for admins only.");
    return 0;
  }
  return 1;
}

Should work.