So, it is definitely a bit difficult to make the right defenses. As the cards will say when you choose them, some are meant to combat certain monsters (stakes/garlic for vampires, guns/rifles for werewolves, zombies, and goo monsters, altars for demons, and bombs for everything). The blocks can be used to seal off certain paths, so you could seal people into homes or try to only let people into certain areas. They will take a few days to make larger structures, but they can eventually work as walls for areas.
Thanks for playing!