Wedging 820 square feet into a 21x20 footprint.
If you leave out trivial things like a washer or dryer ("leave out" is possibly an exaggeration; there are two places where a washer/dryer pair can be placed without too much fussing) and use a tankless water heater and baseboard heat, the 20x21 foot garage can actually make a nice cozy little two-bedroom studio with a ~20x9 workroom on the ground floor.
There's not much room for frills, though, so this structure is pretty much forced into being a modernist (craftsman-style) design.
What, doesn't everyone use lined writing paper to draw up house plans?