when zombies reach or approach a home's entrance, instead of just clawing and hitting it, a roamer should be trying to reach their arms through a space to crawl into and find the smells/sounds/sight
if they're slow and moving towards you, the arms and hands feeling around an area could add to the tension even if its a single one in a room
as others have mentioned, the zeds dont feel threatening and it will be interesting to see what you come up with; i like the idea of scrambling, missing limbs, variations in threat by size, appendages and teeth; runners are a threat only because it's hard to hit them, it'll be nice when they're just unconcerned and the next ones grab and hold on vs just hit
grabbing and holding on to things is a seriously creepy threat