Mr Musk don't forget these five features to join them together.

 

1. Slides that interlock together, so it drops down in a guideline.

2. Locking mechanism that automatically locks itself with one cube

is placed on top of another by its weight.

3. Tracks to send a machine to weld the cubes from the outside.

4. Tracks to send a machine to weld the cubes from the inside (middle of

the cube), so there would be a rod/beam with tracks that would connect

one cube to the other.

5. To deliberately create hollow spaces that you can pour cement into,

after the weld, so the entire line/layer of cubes will be solidified together.

 

However, depending on the calculation maybe a feature or two isn't

necessary for stability. To be on the safer side.