Partial draft with coordinate reprojection
Presently hard coded for latlon->AlbersEqualAreaConic (North American).
Also incldes a *1000 fudge factor for mapproj's non-standard "map co-ordinate" output (otherwise, values were maybe below OpenSCAD's minimum precision - it would crash on output)
Floor and walls don't match up. They should be re-done as extruded polygons rather than corners, using Reproject-ed bounds coordinates. Duh; that will be much cleaner than the present cube coordinate math, esp. for Walls.
Floor now projected
Note that straight line edges may leave feature overhang - consider interpolating along great circles
Walls work with reprojection  now too
(again, as naive straight lines, not great circles)
Record x/y extents as vector rather than separate vars in openscad script
Put extent bounds in openscad vector; used for floor & walls
--projection option
Add other mapproj projections
define Reproject proc dynamically, for less work at runtime
Add --base option for base layer (like floor layer, but without rectangular platter)