Through home schooling I already had familiarity with Autodesk's "Tinkercad" web site, in which my daughter enjoys making 3d printable trinkets-- so I decided to draft some plan proposals there, which I will share with the contracters as I meet with them to get estimates.
Here is an example of one of the proposals. The red is the very edge of the existing house-- to provide context-- while the blue is the proposed addition.