More storage variety.

[The Plum Gate]

Storage compactors: 1x1 ('small' stackable, vertical modular, materials made of metal for thermal transfer), 1x2 ( standard existing ), 2x1 ( flat, stackable, vertical modular ), 2x2 ( square, larger capacity ), 3x3 ( 'large' even more than larger ), 4x4 ( 'huge', biggest single building capacity ).

Gas reservoirs: 5x3 ( existing standard ), 2x3 ( smaller capacity ) - powered variants with higher capacities - compressor oriented design, specialty materials - thermal transfer to environment. 

Liquid reservoirs: 2x3 ( existing ), 5x3 ( larger capacity ). - thermal transfer for both. Insulated variants of both.

Special storage should be removed from first build category. Give it it's own or generalize the storage by category and leave them alone where they are now - make the size selection an aspect of the building material description schema with size selector at the top,  material selection at the bottom.

Categorical storage icons could include a water drop. A gaseous bubble. Bits of solid rubble ( triangle, circle, and square silhouette ). These would take the place of the existing buildings in the plan menu.