Hey Izaqc,
What you need to do is make a building props.
To do this go to your folders in the content browser and Add+ or right click select Blueprint>Blueprint Class then choose building prop.
When its in the content browser, double click on it and then you’ll be able to point it to the model you made in modelling mode, there are also lots of prop settings. Check the collision setting is defaulted with fort in the name, which gives it the ability to be mantled, built on and grapple..ability.
Use the blueprint as the building piece.
To get breakable pieces, with the fortnite damaged wall effect, this is a special material property. If you make instances of the M Fortnite Base Parent material, that has it.
You should be able to find a way to reference your custom materials in them. I have little xp here