The proposed station would weigh 89000 tonnes and provides 60 square meters (646 square feet) of floorspace per person. The radiation shield is made of asteroid rock, augmented by a water layer with 2 % of the mass for neutron moderation, and a thin boron-10 layer for capturing the thermalized neutrons.
Nextbigfuture notes that just bundling 12 Starships in place of each sphere would have a similar volume. The old proposals for using Space Shuttle Fuel Tanks again show how a Starship shortcut for minimal construction could be done. SpaceX Starships are made out of steel, so welding and cutting the steel could be manageable. The outer Starships could be filled with supplies, water and fuel which would make it easy to create the radiation shielding.