There really aren’t many layout tools for DirectGUI, as far as I’m aware.
Aside from just placing things by hand, there are the “a2d*” NodePaths–a set of NodePaths that provide convenient anchors for various parts of the screen. For example, if you want something placed relative to the bottom-left corner of the screen, you might attach it to “base.a2dBottomLeft”.
It looks like we don’t have much documentation on these in the manual (although Google search results seem to suggest that we perhaps used to have more?), but you should be able to find them by going to the API and searching for “a2d”. (Via the search-bar at the top-right.)
Otherwise, I believe that another forum-member made a graphical designer for DirectGUI–you should find it here:
I haven’t yet tried it myself, so I can’t vouch for or against it, but it might be worth looking at!