Choose by the gap in your base, not an unknown rarity
Build a base RNG is about rolling defenses and placing them against waves. Until a complete current catalog exists, the safest comparison is whether a defense helps the front, middle, cleanup, or boss-test job.
Official Roblox media shows multiple visual defense forms across early and later waves. Fresh public guides now repeat names such as Basic Cannon, Crossbow, Catapult, Mortar, Metal Blockade, Gold Block, Witch Brew, Wooden Trap, Wooden Spikes, Golden Mortar, and Wooden Tesla. Those signals are useful for search coverage and player navigation, but they still do not establish exact stats or a full official item table.