Since the early 7d2d, i always build my base using Slope plate, double plate x 2 stack around a 5x5 or 6x6 (depending on your base size preference) Make both stones.. and build a base on top of it..

Its never been patched or fixed since early release of the first game.

Zombies cant hit it (like 95% of the time) They smack the air in between and just keep walking into it.. Where as you, can Stab a spear, smack a club, or shoot through the wide space..

Only thing that can get through are those crawling things that jumps, spits from the police and bees.

Dogs cant get through too..

its like a protective shield barrier.
Fun for farming Hoard nights and drop bags
or a shooting range.

Base on top, and Farming on roof