Disclaimer: Most of the credit to this design goes to madmole.

So you're new to 7 Days to Die and you want to know how to fight off the first blood moon hordes. While there are many ways to go about this, one of the simplest and cheapest structures a new player could erect is the humble 9x9 tower. Take a chair and have a seat follower, I'll show you the tricks up my sleeve.

So you're new to 7 Days to Die and you want to know how to fight off the first blood moon hordes. While there are many ways to go about this, one of the simplest and cheapest structures a new player could erect is the humble 9x9 tower. Take a chair and have a seat follower, I'll show you the tricks up my sleeve.
- You're going to want to start off by digging a 9x9x1 square pit into the ground with your shovel. It should look like this: https://imgur.com/oVTGIOQ
- Now wipe the sweat off your brow and put away that spade. It's building time. Fill in the 9x9 hole with flagstone, and upgrade the two outer layers with cobblestone rocks to cobblestone. You'll see why in a minute. https://imgur.com/5MqZUiE
- Next you're going to erect the two outside layers five blocks high to form the lower base of the tower. Be sure to place and upgrade the corner blocks to cobblestone first, for you won't be able to reach the innermost corner blocks once the walls are in place. https://imgur.com/2W4xAS7
- Nerdpole your way inside the base of your tower and choose one corner for your ladder system to go. Place wooden ladders and a hatch on top. On top of what, you might ask? Why, a ceiling of course! (Just be sure to leave a spot open in the ceiling for where the ladder shaft will go.) https://imgur.com/hnner70
- With the necessary blocks now in place, make your way up the ladder and emerge on to your new second floor. This is where you will make two layers of wood bars placed sideways going all the way around the tower, 5 blocks above the ground; making it two blocks across will lessen the chance of you falling. Add protrusions along the corners to stand on and allow you toss throwables down at the zombies below, like molotovs or pipe bombs. (Be sure you're using wood bars and not wood bars centered!) You can upgrade these to iron bars in the future when resources permit. https://imgur.com/hILSfGQ
- Now it's time to get the third and final story started. Erect 5 block high walls around the edge of the second floor. These don't need to be double thick since the brunt of the zombies' attacks will come from ground level. Leave a spot open on one side to put in a door later on, and spaces for windows in the locations shown, mirrored across all four sides. https://imgur.com/HqMBvJH
- Run along the bars and place sideways-facing poles (not poles centered!) upwards of the window holes. Attach hatches to these poles so that they open upwards, as shown here. Replicate this on all four sides. You can upgrade the hatches later. https://imgur.com/LTujYcD
- Head back on inside and install a door and wooden bars placed furthest away from the player along each square window, as shown in the image. Now would be a good time to add the roof above, but again leave room for another ladder shaft. https://imgur.com/5AePYCK
- While you're at it, place a lip that circumferences the tower on the same elevation as the floor above. On the underside of this lip, place flagstone arch 2m all the way around as shown in the image. https://imgur.com/XplV7ft
- Next, raise a wall two blocks high around the very rim of the top of the tower, and place additional blocks to form a parapet with gaps, forming as the castle battlement. How could one not appreciate a medieval aesthetic touch? Prior to this, adding in second ladder system and a hatch would probably be a good idea! https://imgur.com/7gAnPLc
- You remember the ladder shaft on the one side of the ground floor? Knock out the flagstone block placed at the bottom of the ladder shaft and dig a 1x1 pit down. I chose mine to be 9 blocks deep, with the back edge of stone knocked out and replaced with flagstone to support an extension of the ladder system above. You'll also have to knock out the bottom-most ladder on the ground floor to place in an additional hatch. This is going to serve as the entrance/exit of your tower base. https://imgur.com/KeLriYH
- Climb down to the bottom of the ladder and mine a straight tunnel three blocks high and as far as you care to go. I chose my tunnel to be 24 blocks in length. https://imgur.com/1I5tqTw
- Once you've mined out a sizable tunnel, dig straight up and break in to the surface. Place another wall of blocks on the back side where you will attach a ladder shaft leading up to the surface. You'll want to make this entrance/escape hatch visible, so construct some sort of simple structure that easily stands out. https://imgur.com/YcobmYy
- Now it is time to place the defenses. At this point in the game (day 7-14), you should have a forge going and a fair bit of forged iron produced. Use a portion of this forged iron to craft iron spikes, and use them to surround the base of your tower. I made my single row of spikes two blocks in height, to prevent most zombies from jumping on top of them. If you don't have access to iron spikes, wood spikes and/or barbed wire fences will do for the first couple of hordes, but be sure to place a far greater quantity of them! https://imgur.com/mqGINXj
- There's no point fighting the horde if you can't see the gun right in front of your face. Place some torches around the structure, inside and out, to give you the necessary light levels to face the horde comfortably. If you're concerned about screamers possibly showing up due to the torches, consider turning up your gamma instead, or simply remove some of the torches. https://imgur.com/pDb0uj3
- You're all done! The majority of this tower should be possible for you to construct for the day 7 horde, and as long as you continue to use it, be sure to make appropriate upgrades, such as upgrading the rest of the flagstone to cobblestone, and then the cobblestone to concrete and then reinforced concrete. This design is only intended to do well against the first few hordes on its own, but with the right additions and modifications, it could certainly take you into the late-game, assuming you haven't constructed a much more foreboding base elsewhere by then! https://imgur.com/avRWsp4