How to make your own cloud ? (Not with OwnCloud) [on hold]

I'm very new to web development, yet I have a lot of html/css/php experience. So basically I want to create my own cloud, where a user should be able to authenticate, upload and download files. This is very basic, but I would like to do it myself in order to learn something :) I don't want to use OwnCloud or something similar.

Things I have:

• A local apache webserver running on a windows 8 64-bit system with php and mysql

• A mysql database to store the blowfish-hashed credentials

• another database to store hashed user sessionIDs, used as access tokens (not sure if this is safe)
• A php login/logout system that authenticates the user with his sessionID

Things i want:

• When logged in the user should have access to a certain folder on my webserver (so basically if he enters the url of a pdf.file in this folder, only he can view it, everybody else should be redirected to another "Access denied" html page)
• he also should be able to see a overview of the files in this folder
• uploading should be possible via ftp or the webbrowser directly (this would be epic :)
• downloading is not so important, since there are only pdf files, that can be opened or downloaded easily
• security is very important for me (I just don't know anything here except the basics)
• I also don't want to use Basic Authentication because here I'm not able to style and customize anything

If there is already a article out and I'm sure there is please just post the link because I was to stupid to find it until now... Im glad there is StackOverflow, Thanks in advance ;