For such a small home, you'll find you have
a LOT of choices!
Your 12x12 Cube home is constructed with 2x4 lumber and exceeds code requirements! You'll need to obtain a construction permit from your local municipality for this deluxe cube. As an example: for the City of Nanaimo - ancillary building can be constructed on a lot that is either over 10,000 square feet, on a corner lot, or a lot that has a lane way.
"Low E" high thermal efficiency windows are an option that is available.
The bathroom is complete with toilet, sink, shower. The bedroom is complete with lighting, and shelving.
To ensure low power draw the lighting is all low voltage 12V, either LED or micro bulb. The kitchen is complete with sink, taps, counter, wall cabinets.
Options are available for an induction cook top, or propane cook top, a dishwasher, microwave or a combination microwave/oven/grill.