There really isn't any set directory structure. Solutions and projects can be in any folders. There is a default structure when you create a new solution or project, but it can be changed.
There isn't a "Save As", really. You can copy the solution folder (with any projects it has) to a new folder. Right click on either the solution or the project in Solution Explorer and select Rename if you want to change names. The default is that file references are relative, so you generally don't have to redo file paths.
