I built a web ftp system, that allows me an dmy clients to upload and manage files.
There is a ton of information out there for this sort of stuff.
The only thing I can recommend is find out what control you have over your server. If you are using a dedicated server or run your own then it is fairly easy to do. With PHP using a shared host getting around the restrictions in the .ini file can be a little tough.
Best way to find info is to google the code language and what you want it to do.
for example PHP(this needs to be in all caps) and file uploader, the all caps specifies that you want to look for search results involving that language