Currently 439 Calhoun St. has no garage or shop space, and for me this is problematic because I do a lot of work on my car. Also, my wife and I will have children at some point, and the house also has no room for that. So the basic idea for the addition is to add:
A whiteboard drawing of the current footprint of the house (in brown and purple) is below, plus the general idea for the location of the addition (in orange). Click the image for a larger resolution version.
The picture below shows the side of the house to which the proposed addition would attach. Since the yard is below the level of the house, it seems like it would be reasonable to put the garage at a lower level (~4-5 feet) than the rest of the house, then put the extra rooms on top of it.
The next pictures show the driveway, which would need to be rerouted to the garage entrance. To me it's not clear if it is better to remove the driveway entirely and pour a new, short, straight one that goes straight to the new garage, or if it is better to just wrap the existing one around. Some large trees would need to be removed for an entirely new driveway.
That last picture shows the "laundry room", which could be repurposed to provide access to both the garage and the extra rooms above the garage: two half-staircases (one going up, one going down) could be installed in it. However, the water heater is in that room and would need to be moved.
The last pictures I have are some close-ups of the materials that are currently used to construct the house.
Ideally it would be preferred to use materials that match the existing trim and build quality reasonably closely, but like you said over the phone this isn't entirely possible in general. It appears the siding has been replaced in parts before, so all new siding for an addition would not look too out-of-place. We have had a home inspector look at the place already and his conclusion was (roughly) that the house is of pretty high construction quality and that the original builders didn't seem to cut any corners. I believe the house was originally built in the 1940s.
Below is a floorplan we sketched up for the level over the garage. I don't think it's very good but it's the best we could think of. "MBR" is master bedroom, "BR" is bedroom, "B" is bathroom, "C" is closet. I would definitely want to work with an architect who has a better idea of design than my wife and I, but the general requirements we're shooting for should be about what we've drawn.
The finish of the interior would ideally match the rest of the house. Below are pictures of the floor throughout the house (hardwood is fine, no need for carpet), the wall trim, and the bathroom trim.
Thanks again!