Hi I am trying to create a large hollow sandstone object (it will be full color). I want to make full use of the print size and my model nears 20cm cubed - and is hollow. My questions - How thin can I realistically make the walls of this model. Is the price calculation on this model taking into account the hollowness? Any other tips that I can glean? Many thanks, Matt Heres the link https://www.shapeways.com/model/430152/d91c75a243c0d867a8e6ff f68136fa64/chaossphere_20cm.html?gid=ug