Hey Rojo - I'm just making them by hand. With only 12 layers per floor that means any given decoration etc only has 12 slices to worry about. I draw most features first as a standard sprite (how I want it all to look at the end) before drawing the 'slices', which gives me a good guide on dimensions etc. It's some trial and error - and some stuff just looks horrible.
I Googled Paster - it might actually solve some of the issues I've got with using canvassnapshots as I am at present. Great work!