I have a master template that contains hand coded HTML, JS, and CSS (that worked in 3.7) that I would like to use as the template for a Sitefinity 4.0 project but I cannot seem to figure out how to create a template and use that master file instead of dragging and dropping, painfully, a bunch of layout boxes and re-crafting all my existing code. Whereas I could drop my master in to the project from the file system on 3.7 it doesn't seem to find it, or allow me to use it in 4.0
Specifically- I can't seem to get the paths to the JS and CSS files correct in the HTML. Firebug says that the server is returning a Forbidden and Not Found for certain files.
You can use your existing master page, however in 4.0, they don't automatically pickup as they do in 3.x. Instead you first create a design template, choose that master as the base. there should be an option for "choose your own master file".
here's a link to the documentation for this: http://www.sitefinity.com/4.0/documentation/Designers-Guide/creating-a-template/creating-a-template-using-master-pages.aspx
hope this was helpful!