How can I Create a 3D gaming app where the user can create a World from predefined shapes in the app?

Create a 3D gaming app where the user can create a World from predefined shapes in the app and a 3D avatar / humanoid can visit and explore and interact with this World. In this World creation app there will be a land where the World will be drawn and a plus icon which will open a drawer/inventory, which will have some predefined shapes of the components like building, car, road, trees etc and these shapes should be draggable to the PlayGround to create building. Once World is created, the user's 3D avatar should have the liberty to visit the World.,Create a 3D gaming app where the user can create a World from predefined shapes in the app and a 3D avatar / humanoid can visit and explore and interact with this World.