here is a good php file uploader script example that you can use in your  website

it is secure and can create folder for registered users and upload their files into it

here is the php code :

//start session and capture username that we will need later
session_start();
$user = $_SESSION['username'];
//after submiting form create folder for each users and then execute next function
function makedir(){
global $user;
	if (file_exists("upload/".($_SESSION['username']))) {
		upload();
	}else {
		mkdir("upload/".($_SESSION['username']), 0777);
		upload();
	}
}
//upload function
function upload(){
global $user;
// prevent files which are not png jpg
if (!(($_FILES["file"]["type"] == "image/png") || ($_FILES["file"]["type"] == "image/jpeg") || ($_FILES["file"]["type"] == "image/pjpeg"))){
 echo 'invalid file';
//100KB max file size
}elseif($_FILES["file"]["size"] > 103000){
 echo 'too big';
//everything is OK
 }else{
   if ($_FILES["file"]["error"] > 0)
     {
     echo "Return Code: " . $_FILES["file"]["error"] . "<br />";
     }
   else
     {
      //save extension of file
	  $exts = explode(".", $_FILES["file"]["name"]) ;
	  $n = count($exts)-1;
	  $exts = $exts[$n];

	 //characters that will be needed to renaming file after upload
	 $chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
	 //generate random string with minimum 5 and maximum of 10 characters
	 $str = substr( str_shuffle( $chars ), 0, 10);
	 //add extension to file
     $name=$str.".".$exts;
	 //check if file exist (there is almost 0 possibility )
     if (file_exists("upload/".$user."/" . $name))
       {
		die("please try again");
		//move uploaded file to right directory
       }else{
       move_uploaded_file($_FILES["file"]["tmp_name"], "upload/".$user."/" . $name);
       echo "Stored in: " . "upload/".$user."/" .  $name;
	   }
     }
   }
}

if(isset($_POST['submit'])){
//after submiting execute this function
makedir();
}

and html code

<form method="post" enctype="multipart/form-data">
 <label for="file">Filename:</label>
 <input type="file" name="file" id="file" />
 <br />
 <input type="submit" name="submit" value="Submit" />
 </form>