Creating new XMLFile programatically

I'm trying to create a new XMLFile and marshal the DomElement model that I have into it. Going through the forum and also the guides, it's assumed everywhere that I have the XMLFile (assuming by using PsiManager) and modifications happens afterwards. In my case, the file doesn't even exist and I don't see a way to create the XMLFile. 

So my question is this: if I want to create the XMLfile, do I have to first create the file and add the parent tag there and then read it using PsiManager? or there is a better way of doing this.