I've been playing a bit, and my recent base that I built didn't survive the day 14 horde on standard difficulty navesgame.
I decided to build a pillbox/like bunker using salvaged cement mix from some nearby POIs. It took awhile, and I had some suspicions about how well it would work, but I wanted to give it a go anyways. My walls were 2 blocks thick, with flagstone blocks for the knee level and reinforced cement for the shoulder level. I had some "murderholes" that I could use to shoot down at zombies. I also used some spikes to slow them down before they got to the walls.
It held out ok, but at around 1:45 they tore through the second layer of my walls and swarmed in. There weren't even that many zombies at a time (standard settings), but the damage added up.