You really just need enough shavings to start with, so that the floor is fully covered, even if the shavings shift around as the chickens move around. If you notice bare spots from the chickens kicking the shavings around at first, then you need to add more shavings, at least in that area. You don't want to be able to see the floor through the shavings or any bare patches.
If the coop starts to smell or areas look too poopy, either clean it or layer clean shavings over those areas, depending on how you choose to manage your coop.
If the coop starts to smell or areas look too poopy, either clean it or layer clean shavings over those areas, depending on how you choose to manage your coop.