I had this working at one stage on custom blender imports.
I removed them and opted for fortnite assets because I couldn’t get my walls to fall down when supporting walls were destroyed (deep settings I couldn’t find).
Found the old forum thread (hopefully it still works with the latest update)
-Create a new BluePrint, selecting the Building Prop Option.
-Open it up and point the mesh component to your mesh.
-Click on Class Defaults (above viewport menu bar)
-Then in Details, check Do Not Block Building
-Check Structurally Support Overlapping Actors.
-Compile BluePrint and close.
-Drag the Blueprint onto the scene.
Player builds are 512 wide and 384 high, so if you want to keep everything flush and level put your walls at multiples of 512 for x or y locations, and 384 for z locations.
And if you want the cracking effect for breakable walls check this thread…however we could never work out how to get them to break when a supporting structure was destroyed, they just stay up in the air looking silly.