A lot of work imo, if your new to Construct 2 I would start with something smaller just to under how it works.
If I was to do a dune game I would use drag a drop behaviors which are disabled once "dropped" and you can do test on clicked HUD options if you have the "credits" spawn that building for example. Then you can do things like clicking a building changes HUD, and building units spawns sprites/units at building UID.
As for the perspective, keep it simple by imaging everything is flat but your asset are actually in isometric. I would use collision to stop buildings being placed over it other.
Or you can use one of the plugins to handle isometric/perceptive grids.