Add a "mirrored" mode to the "Lab" make maker. Many maps are symmetric, and without this tool/mode it takes more than twice as long to make such a map, because not only do you have to do everything twice, you have to take extra time to make sure that everything is perfectly matched.

As it is, we can't even make half-maps and paste them rotated as prefabs, because there's not a 'ctrl-a' equivalent to select everything that needs to be part of the prefab.