How can i improve this piece? comments and tips?

Hey everyone.

This is my first piece, and its kinda meant to be a rubix cube house (for kirupaville). Im finding it hard to get the borders and shading right, and the plot looks a bit empty (it’s a 1x1 grid).

Here is an example of my workings.

Any suggestions to improve, and make it look more like a rubix cube?