Hole in a non BSP object

I have made models of walls and windows. They measure 1x3mx10cm. The idea is, a user drags and drops in a wall and copies it as many times as they want. Then they take a window and drop that onto the wall and the part that the wall that the window is touching becoses transparet, so we can see through it. In Blender (which I used to make tehse) you can just use the boolean tool and it makes a hole. But I don’t know how to achieve this in UE 4, I guess it could be made so the part of the wall’s texture that’s covered with a window just becomes alpha transparent.

So for those who still don’t understand, here’s the short version: I place down wall 1. I take window 2 and place it on the wall. I want the part of the wall that the window coveres to become a hole. Just like BSP subtractive brush, but on 2 objects that are imported obj’s, not BSP’s.

Yes, I know I could go make the holes in the walls straight in my modeling app, but that would take alot longer, plus the user won’t be able to decide exactly where to place the window.

I am not familiar with UE 4, but I have alot of models gathered up over the years. Most of which are connected with architecture in some way or another. So, if you take your time to answer my question, keep in mind, I only know the basics of material in UE 4, so explain to me what to do like you would to a 3 year old.