I wanted to create an alien species that mostly relies biomaterials and biotechnology and one method of growing hard materials could be controlling the growth of seashells. The alien mollusks will be based on earth mollusks for this question.
At the earliest stages when the species is as advanced as stone age man, they could manipulate the mollusks whilst in shallow water to create simple structures. When they evolve into an advanced species they could have mineral rich vats of liquid with complicated shell structures being created which can be used for many purposes or even combined with other biological material to give other useful properties.
At first the alien species will try to manipulate the shells into small tools, around the same size as the shell would be and they will try to make large (possibly curved) sheets of shell. The larger sheets may need multiple mollusks working together or breeding much larger mollusks but either way they will need to be manipulated or tricked into making the shells these different shapes.
How can this alien species when at the stone age level, manipulate the mollusks to make these different shell structures?