I have seen the mod to modify the area build. The template can be a line or a sphere. But the entire template is filled with the same building. I wonder the mod can modify the area build to contain multiple types of buildings. For example, when a player drags a line of turrets, the area build command also builds the walls to protect the turrets. Is it possible?
Not with the built-in placement methods. Between the newer raycast and orders apis is probably possible to calculate the positions.
with the new APIs it is very certainly possible to make an arbitrary template system that even shows previews while placing the template via puppets.