Build a Base RNG: Best Beginner Base Layout for Wave 300

Reaching Wave 300 in Build a Base RNG as a new player comes down to one repeatable layout. A U-shaped back wall paired with two forward-facing side wings gives your turrets overlapping fire lanes, funnels enemies into a killbox, and keeps your core protected long enough for damage to stack up. The build works with the common weapons most players roll early, so you do not need rare pulls to make it survive.

Quick answer: Upgrade Plot Size to level V in the Skill Tree, place blocks diagonally on both sides into a U-shape, raise the wall two blocks high, then fill it with Rusty Mortars and Bamboo Shooters in the center, Slime Cannons and barrels on the side wings, and Wooden Teslas flanking the core. Elevated corner platforms hold extra Mortars and cannons.

Upgrade Plot Size before you build

The full layout will not fit on a default plot. Open the Skill Tree, go to the Base section, and buy Plot Size upgrades until you reach Plot Size V. This is the single most important prerequisite, because a cramped plot forces you to cut wings or turret rows that the design depends on.

Plot Size tier	Coin cost
Plot Size I	7.5K
Plot Size II	15.0K
Plot Size IV	200.0K
Plot Size V	500.0K

Tip: Let your base farm coins offline to bank the 500K for Plot Size V faster. The base keeps fighting and earning while you are logged out, so a full plot upgrade is often waiting for you when you return.

Build the U-shaped wall

Enter Build Mode and use Clear plot to wipe any old placements. Starting clean stops leftover blocks from blocking your diagonal lines.

Place 2 blocks on the left edge, then run blocks diagonally up and to the right. Mirror this on the right edge, running blocks diagonally up and to the left. The two diagonals angle inward toward the back.

Connect the two diagonal ends at the back with a row of 4 blocks. This closes the shape into a U, with the open side facing incoming waves.

Layer the whole U-shaped wall so it stands 2 blocks high. The extra height blocks enemies from clipping over the barrier and gives raised turrets a wider firing arc.

Place the core weapons inside the U

Add a single row of blocks inside the U-shape to create a raised platform for your main damage dealers.

Put your best turrets in the center back where they have the longest line of sight. Bamboo Shooters work well here. Set your second-best turrets, such as Rusty Mortars, on either side of them.

Place Wooden Teslas inside the U-shape, one on each side of the central weapons. The Teslas add chain damage close to the choke point where enemies bunch up.

Mortars have range and splash, so they perform best from the back rank where they can lob shots over the front wall onto grouped enemies. Keep them behind your shooters, not in front of them.

Extend the side wings and corners

Build two parallel walls forward from the U-shape, one on each side, placing 6 blocks per wall. These wings extend your coverage down the lane and slow enemies before they reach the core.

Top the side walls with turrets. Slime Cannons are a strong pick because they slow enemies, buying time for the rest of your base to fire. Slime Barrels fill any remaining slots.

Line the outer edge of both side walls with 6 Rusty Steel Barrels each. The barrels add another layer of damage along the flanks.

Build elevated platforms on the outer corners of the side walls using Stone Blocks. If you own barricades or spikes, use those instead for extra durability.

Place Slime Cannons and Mortars on top of the corner platforms. The added height lets these turrets fire over the front walls and cover more of the approach.

Stack any remaining blocks and weapons, including spare Mortars, along the front-facing walls to close the layout. Use delete mode to remove temporary placement blocks and tidy up turret spacing.

Weapon roles at a reference

Weapon	Placement	Role
Bamboo Shooter	Center back of the U	Main damage down the lane
Rusty Mortar	Inside the U, back rank	Splash damage on grouped enemies
Wooden Tesla	Flanking the core weapons	Chain damage at the choke
Slime Cannon	Side wings and corners	Slows enemies for crowd control
Rusty Steel Barrel	Outer edge of side walls	Flank damage layer
Stone Block	Outer corners	Elevated platform base

How to know the layout is working

Start a wave and watch where enemies die. A working build stops most attackers before they reach the back row of the U, and your core turrets should stay intact through Wave 300. If the base holds and the wave counter keeps climbing without losing your central blocks, the setup is tuned correctly. Turret quality still matters, so higher-rarity versions of the same weapons push you further past 300.

Common reasons the base fails early

Skipping the Plot Size V upgrade, which forces you to leave off the side wings or corner platforms.
Leaving the wall one block high, letting enemies pass over the barrier.
Putting Mortars in front instead of the back rank, wasting their range and splash.
Not placing slowing turrets like Slime Cannons at the front, so fast enemies rush the core before your damage lands.

Once the layout is holding, keep feeding coins into Index unit upgrades and rolling for better weapon rarities. The frame stays the same. You are simply swapping in stronger versions of Mortars, shooters, and slowing turrets to reach deeper waves.