Presume that you will use mysql to store user data such as their login details, and php to validate the login.
You can also store the path to the personal dir in the database, or just use their username if you have enforced uniqueness there.
PHP has a full set of file system functions to manage the creation and checking of folders. By concatenating their personal info with a base path, you can generate the save path at run time, as well as list contents etc.
If you want to use .htaccess for login then you can also configure it to set path vars and write access to individual folders per user.