There are a lot of tools available that can do that for you, I think there's no need to develop this yourself. If you still want to make this yourself I'd use a File System Watcher to track changes in a certain directory and keep a list of changes in memory. The periodically send the changes files (for example using FTP) over the line.
Some tools I found so far :
http://sourceforge.net/projects/freefilesync/[
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http://www.csync.org/[
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I've recently been using a program called SyncBack, it's good!!
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