Thanks for the tips people.
We intend to make some changes to the Jacobs house interior design, but try to leave the exterior as original as possible. We'll have to use Butynol on the roof and create guttering, as well as incorporate a 50mm drop from the interior to the exterior

The guttering will drain down chains not pipes, and into wide concrete bowls sitting atop the drains - a legacy of the house I grew up in.
We'll stretch the lounge to be 6 metres deep (it's 5 metres on the plans) thereby extending the size of the dining space (We won't be incorporating any built-in furniture except the desk in the corner of the lounge.) and increasing the living area.
Open fires are banned in my city, and even a gas fire seems irrelevant in the days of Heat Pumps and water-solar heating of the floor slab so we are going to dispense with the monolithic fireplace and chimney. We plan to rotate the kitchen 90 degrees so it faces directly into the lounge - becoming the centre of focus for the living area. (My Partner Emma is a wonderful cook and entertainer and spends a lot of time in the kitchen.)
To me, this makes sense. I know FLW was intent on focusing on the Hearth back in the day - but this ignores the huge change in living styles and pollution caused by open fires, and even log burners.
Because in 1936 there was no concept of the TV, or stereo we are going to re-work the end of the lounge, while keeping the "breaking the box" corner . We'll try to work a plasma TV into the wall and incorporate a set of electrostatic 5.1 surround sound speakers into the plan in an unobtrusive way.
We like the idea of an ensuite bathroom, and therefore will extend the end of the bedroom wing and convert the Study into the Master bed. This extension will allow me to incorporate a single longish garage (which will be *my* "workspace"!) towards the rear of the house. I'm hoping the garage will be almost invisible from the street, with it being recessed back behind the car port. The Garrison House Project (Michigan) plans more closely reflect how we'll deal with the master bedroom.
I investigated the option of having the windows and doors done in wood - but the cost is absolutely prohibitive. (In 1936 it seems like materials were expensive, but labour was cheap - and now its the materials which are cheap and the labour expensive!) I'll be forced to use aluminium doors and windows, but we'll use a color which is sympathetic with the design.
FLW originally called for (IIRC) Cypress and Redwood coverings on the exterior walls but we will use Cedar and Redwood. Inside walls will be the standard plasterboard, excepting the bricked sections which will remain revealed. Against the rear wall of the lounge (where the clerestory windows and the book shelves are) we may well repeat the exterior finish as a feature wall.
We'll require more storage than FLW allowed for and this will be partially achieved by overhead storage in the garage, an increased depth to the cupboards ajacent the dining area. The kitchen will be extended 1 foot (Hate that imperial measure!) because we will have no basement at all so the stairs can go - and the bathroom will also be extended by 1 foot.
You are correct about the size of the house: the squares are 4 x 2 feet (ACK) which conveniently translate to 60cm x 1.2 Metres which is perfect because materials still coming in 2.4 metre lengths...
The Jacobs floor plan (original) is almost exactly 1500 square feet, which equates to 139.8 square metres. Our architect is adding another 30 sq. m to the plan and the building cost is above average too. Here in New Zealand a "typical" new home (i.e. a crappy and ugly box with a pointy roof) costs $1000 per square metre. Our home will cost around $1130 per square metre. This will bring the cost of the building to approximately $192,000. Sitting atop the $150,000 section we *hope* the property will be valued at over $400,000 by the time the landscaping is complete.
We only intend to live in the house for about 8 years - or until we have a child over the age of 7 or 8 - at which time we'll investigate building another usonian.
Currently the link above is dead - but I'll keep trying it - and order the book when possible.
Have no fear - as the project progresses, I'll be posting our final plans, drawings, perspectives, 3D models, section photos, construction photos, detailed accounts of the building process, and make it all available for anyone who wants it. I have Gigs of space on my server, so you'll probably end up being sick of me and my bloody house by the time its finished!
Oh, I should add that Christchurch New Zealand is on the coast of the Canterbury plains. It is pancake-flat running up to the southern alps 60 miles away gaining altitude gradually the whole way.
The Jacobs house design is therefore ideal for the city, which is also sprawling and flat, (400,000 pop.) and will fit in with the environment wonderfully.