[Zope] DocumentLibrary or new product ?

Hi, I need an application similar to DocumentLibrary. But I have to make some modifications: 1. I want to assign user rights for a specific topic (folder) 2. The files should be stored externally and not in ZODB. 3. I want to specify, which document types are allowed in a topic (folder) Is there a chance to modify DocumentLibrary to fit my needs or would it be better (easier) to code a new product? TIA Frank