I actually investigated this, and the approach that would have to be used would be - very complicated to say the least. https://en.wikipedia.org/wiki/Gastropod_

I actually investigated this, and the approach that would have to be used would be - very complicated to say the least. https://en.wikipedia.org/wiki/Gastropod_shell https://en.wikipedia.org/wiki/Gastropod_shell https://en.wikipedia.org/wiki/Mollusc_shell https://en.wikipedia.org/wiki/Mollusc_shell A good starting candidate for genetically re-ingeneering would be the near extinct giant clam. https://en.wikipedia.org/wiki/Giant_clam https://en.wikipedia.org/wiki/Giant_clam First you would need the genetically altered reduced snail - organ connected to a moveable scaffold that has the length of the longest wall you would want to extrude. You in addition would need: Some machinery to support the organ and to supply the nutrients necessary for building up such a structure. Also do not forget that the extruded shell material is flexible at the start and hardens out. Another problem - the shells are rather brittle so additional material to fill the spaces between shellrooms would be needed. Im not that well with economics, but if somebody would take this wild ride through a pseudo buisnessplan, that would be fun.