In doomsday, my construction master is vertical not diagonal. Scrolling through it says can build..

In doomsday you can build up to 4 Immunity research facility buildings. 1 can be placed at each of the 4 alliance centers (if your alliance has built 4). This is not dependent on Specialty points.

In the Blue Construction Specialty section there are 4 paths, Up, Down , left and Right. The down path will let you unlock the extra Assault and guardian fortresses to place. The path to the right has items that will let you add bonus immunity points depending on the number of research facility structures your have built.