I’ve created a simple building in Blender, applied a solidify modifier and then cut out a window. however, when importing in to unreal the window is not a real hole, when shooting bullets at it for example it just bounces off instead of going inside the cube!
Any idea what im doing wrong??
You need to generate a more precise collision volume for the building. It’s probably using a simplified box for collision at the moment.
Amazing, thank you so much that solved the issue. I had to search for a UE5 tutorial but managed to fix it by switching the Collision complexity to Complex 
You can also use the UCX_ prefix to make a fully custom collision mesh in blender and export it with the model via FBX
Look at the collision section of the documentation for details.