decay stratergy

for my project i am going to make it that humans all died out in the worst storm man kind has ever seen. my island is going to be flooded (mostly) and there is going to be perpetual rain and thunderstorms. i am going to show the big concrete structure collapsing from the rollers underneath it giving way and i am going to show some of the walls within the building collapsing. i feel like 100 years wouldn't be enough for all of the structural issues to take place so its only really the outside walls that faced the full brunt of the storm and the big structure that i am going to show collapse. i am going to take the exact same shots when i do the before and after the storm to fully show the change.