Because I don't actually know the dimensions of the original building, and I have used reference with photographic distortion, I am allowing for a certain degree of 'creative freedom'.
Dimensions are as important (probably more so) than silhouette, so I'm goint to put a human scale reference in there to check I'm happy with the actual dimensions I've quickly blocked out.
The dimensions dictate to me the texture requirements, since I'm working to 128 pixels per meter, therefore, 4 m x 4 m will require a 512 x 512 and a 2m x 4m will require a 256 x 512.
I will work to 1024 but the final textures will be the above dimensions ingame. I have approx. 1200 polygons for the buildings - this hopefully should give me enough to cut in detail along the roof/gables and shed.