UNIX for Dummies Questions & Answers

I am interested in knowing the proper, yet security-conscious settings for a directory. Here's my scenario:

1. I have a username for FTP access to my server called "user".
2. For the purpose of the scenario, PHP runs as "nobody" on my server.
3. I have a directory off the document root called "sample".
4. The "sample" directory is chmod'd at 0755 (drwxr-xr-x)
5. "sample" is owned by "user" and the group is set to "user" so it looks like this:
drwxr-xr-x 2 user user 4096 Dec 21 10:30 sample

The above is all very straight forward and standard.

So I want to have a PHP script be able to create (mkdir) and delete (rmdir) directories under "sample". Yet, I don't want to obviously overly expose my server by opening up the permissions (I could easily chmod sample to 0777 and make it world write-able).

What is the best combination of permissions, owner settings and/or group settings to allow my script to create and delete directories under "sample" while retaining the ability for "user" to continue to FTP into the directory? I also will have a PHP script that creates, updates and deletes files in the directories in "sample" that will need to allow "user" to gain full FTP access to them.

I have tried each of the following in PHP scripts and I continue to get "Operation Not Permitted" errors:
> shell_exec('chmod 0777 newDirectory');
> shell_exec('chmod 0777 newFile');
> shell_exec('chown 0777 newDirectory');
> shell_exec('chown 0777 newFile');
> shell_exec('chgrp 0777 newDirectory');
> shell_exec('chgrp 0777 newFile');
> chmod('newDirectory', 0777);
> ftp_site($conn_id, 'chmod 0777 newDirectory')

Nothing seems to work.

Thanks for helping.