also, a folder icon most likely already exists so browse through them to see which you can use instead of having to draw one. to browse through them I recommend you open the default web browser and type / in the address bar. you can then navigate to the icons directory and view them right there in the browser.

as you probably already know you can quickly get to the icons in the browser by putting this in the address bar

file:///usr/share/icons/hicolor/48x48/hildon

for example
filemanager_media_folder.png
is a folder icon you can use.