File photos = new File(getFilesDir(),"photos");
   photos.mkdir();

AlertDialog.Builder alert = new AlertDialog.Builder(this);

alert.setTitle("Title");
alert.setMessage("Message");

// Set an EditText view to get user input
final EditText input = new EditText(this);
alert.setView(input);

alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int whichButton) {
       String value = input.getText();
       // Do something with value!

       //This is where you would put your make directory code
       File photos = new File(getFilesDir(),value);
       photos.mkdir();
    }
});

alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int whichButton) {
        // Canceled.
    }
});

alert.show();

String value = "directory to create"
File photos = new File(getFilesDir(),value);

if(!photos.exists())
{
    if(photos.mkdir())
      {
       //directory is created;
      }
}

AlertDialog.Builder alert = new AlertDialog.Builder(this);

alert.setTitle("Title");
alert.setMessage("Message");

// Set an EditText view to get user input
final EditText input = new EditText(this);
alert.setView(input);

alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int whichButton) {
       String value = input.getText();
       // Do something with value!

       //This is where you would put your make directory code
       File photos = new File(getFilesDir(),value);
       photos.mkdir();
    }
});

alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int whichButton) {
        // Canceled.
    }
});

alert.show();