Build a voxel scene by using the free to use Editor Magica Voxel and just submit your vox file in the customer content section.
We will review the creation and unlock it to everybody in the game. (give us 1-2 days to do this)

Guidlines:
All buildings must match the world size. 1 Voxel side represents 1/2 meter (1/2 yard).
So a building floor is around 5-7 voxels hight. A standard door has a height of 4 voxel.
The game world is split in tiles. One tile has the size of 30 x 30 voxel. Each building size is definied by the number of tiles. A Custom scene for a 2x3 building must have a voxel size of 60x90.
The look of the building should match the game stage. So no modern villa in early game.
No offending design.

1. Select under "Choose building to customize" the building you like to customize. The buildings will be unlocked step by step.
2. Design a building and scene in Magica Voxel with the definied size of this building. Make it look nice and detailed :-)
   The lowest voxel layer (ground) on z=0 will be your ground texture. Tip: Each voxel on this floor with the color of "30 124 12" will be rendered transparent. Can be used to match environment.
   You can test your creation and ckeck how it will be rendered under "Quick preview"