A three-storey tower modelled on a Japanese castle keep (tenshu). White bone-block walls with stripped oak posts, dark prismarine stair eaves wrapped around each floor for a teal-tile look, storeys that step in as they rise, and a hipped roof that closes in from all four sides. 23 layers, 2,461 blocks.
In the short, the castle grows through three sizes — small (217 blocks), medium (777) and large (2,461). This pattern is the largest. The ground floor is 17 × 17, the upper two are 15 × 15, and the roof alone is 944 blocks, 38% of the build.
Layer by layer — wide ground floor, narrower upper floors, then the roof
LAYER 1 — floor. Fill 17 × 17 with 289 spruce planks.
LAYER 2–5 — ground floor. LAYER 2 is a 59-cobblestone base with a stripped oak log post in each corner; LAYER 3–5 are bone-block walls (59–60 each) with the same four posts. LAYER 5 has 16 glowstone inside as ceiling lights.
LAYER 6 — second floor and first eave. Lay a 15 × 15 floor of 221 spruce planks, then ring it with 72 dark prismarine slabs and 64 stairs out to 19 × 19. This is the widest layer of the build, and the eave jutting out over the ground-floor wall is what makes it read as a castle keep.
LAYER 7 — second eave row and second-floor base. Another ring of 64 stairs at 17 × 17, with a 52-cobblestone base and four posts on the 15 × 15 inside. Every stair faces down and outward.
LAYER 8–10 — second-floor walls. 52 bone blocks and 4 posts per layer, one block in from the ground floor. 15 glowstone on LAYER 10.
LAYER 11–15 — third floor. LAYER 11 is a 15 × 15 floor of 221 planks, LAYER 12 a cobblestone base, LAYER 13–15 bone-block walls like the second floor. 15 glowstone on LAYER 15.
LAYER 16 — roof base. Step back out to 17 × 17: a 13 × 13 core of 169 dark prismarine, edged with 56 stairs and 64 slabs.
LAYER 17–23 — hipped roof. Each layer steps in one block on every side — 13 × 13, 11 × 11, 9 × 9, 7 × 7, 5 × 5, 3 × 3. Fill the inside with dark prismarine and edge each layer with outward-facing stairs. Cap LAYER 23 with a single prismarine block.
How much material?
Dark prismarine is the big one — 455 blocks, 352 stairs and 136 slabs. Stairs are 6 blocks for 4 and slabs 3 blocks for 6, so that is about 1,050 blocks in total. Each dark prismarine is 8 prismarine shards + 1 ink sac, so roughly 8,400 shards — a full ocean monument raid. In survival, see the substitutes in the FAQ.
Spruce planks, 739 is 185 spruce logs. The 48 stripped oak log posts are oak logs right-clicked with an axe.
Bone blocks, 491 take 9 bone meal each — 4,419 bone meal, about 1,473 bones. White concrete or quartz blocks look almost the same.
163 cobblestone, 46 glowstone (184 glowstone dust), and the furniture — 12 bookshelves, 6 furnaces, 6 white wool, 3 crafting tables, 3 flower pots — are small. Furniture can be swapped for anything of a similar colour without changing the outside.
Tips
The eaves (LAYER 6–7) are the heart of this build. Every stair must be placed low side outward so the tiles look like they run off the roof. Finish one side, check the direction, then go round the other three. Corner stairs bend automatically, so place them last.
From the second floor up, the walls step in one block (17 → 15). Put the posts in their new positions first and the wall outline takes care of itself.
Once LAYER 16's 17 × 17 is right, the roof is just stepping in one block on every side per layer. You can skip the solid core and place only the stair edges — it looks the same from outside and saves nearly half the roof material.