Each metaverse has its own building system. Decentraland uses the Builder (drag-and-drop, browser-based) for simple scenes and the SDK (code-based, TypeScript) for interactive experiences. The Sandbox uses VoxEdit for 3D voxel assets and Game Maker for assembling them into playable experiences. Spatial uses Unity integration. Start with the platform's official tutorials — they're free and take 2-4 hours.

For custom buildings and objects, Blender is the go-to free tool. You don't need to become a 3D artist — learn the basics: modeling a building, applying textures, UV unwrapping, and exporting as GLB/GLTF. Blender Guru's 'Donut Tutorial' on YouTube is the classic starting point. Focus on low-poly models since metaverse platforms have strict polygon limits.

Decentraland limits each 16x16m parcel to ~10,000 triangles and 10MB of textures. The Sandbox has voxel limits per LAND. Spatial has polygon budgets per room. Design within these constraints from the start — building something beautiful in Blender that exceeds the platform's limits means rebuilding from scratch. Use texture atlases and low-poly techniques to maximize visual quality within the budget.

Static builds are forgettable — interactivity is what makes people return. Decentraland SDK uses TypeScript for clickable objects, NPC dialogues, mini-games, and token-gated areas. The Sandbox Game Maker has visual scripting (no code needed) for triggers, rewards, and game loops. Start with simple interactions (click to open a link, walk-through tour) and build up.

Test locally first using the platform's preview tools (Decentraland has `dcl start` for local preview). When ready, deploy to your parcel. Walk through the entire experience on desktop and mobile (if supported). Check load times, polygon counts, and interaction triggers. Have 3-5 people test it — they'll find issues you missed because you know where everything is.