This is something I've always wondered how to pull off and I've definitely seen it in a video before but how do I make part of a building look crumbled or eroded away? I have an Aztec themed inverted coaster still under construction and the station building has a chunk deliberately missing (as it's right on the edge of a cliff) so instead I want that part to look it's crumbled over the side and all I've done so far is just arrange some small rocks into a pile around that area. Anything else I need to do to make it seem more realistic? 