I'm implementing a web application like that right now, using CGI::Application. Here's the data structure I've set up (with tables capitalized): Users can have multiple Memberships in any of a number of Projects; Files are uploaded to a specific project by a specific user.

There's more detail, like having some users be staff members, with the ability to create new projects and new users. Staff members can also be managers for a specific project, allowing them to add/remove/create project members.

But like the first respondent said, this is really a data modelling question and not a Perl question. So good luck with that.