visual menu/folder structure

I have a formfield of textbox. People type the folder structure in that textbox. eg. / or /folder1/ or /folder1/folder2/, etc. I do not want that the users should type this in the textbox directly. I want to have a button that should open a modal window so users visually via mouse and keyboard create new folders/subfolders structure. Then close the window to display the folder/subfolder entry into the textbox as /folder/subfolder/subfolder1/ Note: You are not to create any folders via the code. This is a just a concept to prevent users typing in /folder/subfolder/subfolder1/ themselves in the textbox.