widget needs write access

I have a user control turned widget that grabs certain XML sources and combines them into a single XML file on my website. I'm running into permission problems. The user control can't overwrite the file. Similarly, if I try to view the XML file straight from a browser, I don't have permission to view it. It works fine in development on my local computer but won't work in production. The file is saved at the root of the site. Is there a specific location where I should be saving files like this?