This can't be treated as meaningful, given other projections and goals (Mars colony, etc.).
Although realistically this will be built from lunar materials, you still need to lift a lot of mass to build the necessary industrial processing and mass drivers to launch it from the Moon to some Lagrange point.
And there are many other useful space megastructures that can be built in space from common materials, like giant solar arrays beaming power down via microwaves: https://en.wikipedia.org/wiki/Space-based_solar_power
Most of these proposals date from even 1980s.