I'm sure this must have been brought up before but I would love to see an option to rotate the structure you are building (or, rather, choose which way you would like it to face) when the building process begins.
It would be very simple to flip the sprites obviously, the only thing that would have to go into coding really is to set the house facing South (default is East) to the correct door position.
There could be a little visual window showing two images of a cabin/oven/etc that makes you select which way you'd like it to face (South or East) as well as adding the materials (Like having two house pictures above the materials list on the build menu).
------
Main issue I see is the shading/lighting on the structures themselves. (Pointed out by Chakravanti)