easiest just to upload your rough design and get an estimate. Block it out using basic shapes, upload it and get a cost estimate. You can be confident the estimate will be the upper bound, assuming your final design scale doesn't change drastically. if estimate is acceptable, proceed with final design.
most 3d packages should have a measure tool to give you basics like bounding box dimensions, volume, and surface area. leverage that as you are designing.
Porcelain is a little weird. Spec sheet says maximum wall thickness is 50mm. but in reality it's any section of volume must be less than 50mm in the longest dimension. e.g. a slab that is 100mm x 100mm x 50mm would likely get rejected as the longer dimensions exceed 50mm. Only reliable way to check it myself is having a 50mm cube that I move around inside the design and make sure there're aren't any chunks larger than the cube.
Last edited: Oct 21, 2016