shielding

Covering the entire habitat assembly with two meters of concrete
isn't necessary.

Two feet of an iron-concrete mix is ample for those areas where life
is expected to exist to any extent and even the duration of time that
this life is there is part of the math. So, where life may only be a
few hours at the most, you can do with just a foot thick of iron-
concrete. This if for normal space radiation of course.

Space suits, for example, are only meant for a few hours of EVA.
Time is part of the picture (cost-savings wise, but also important to
bio units).

Now, again, this is for normal space radiation.

For solar flares and cosmic radiation, you have shelters within your
ring assembly (preferably equal-distant apart for a more stable spin)
with two feet thick walls of iron-concrete. Within these shelters
you always hold navigational and radiation-sensitive electronics, as
well as enough foodstuffs to last a week or more, etc.. and just
enough space for navigation, attitude control, eating, sleeping,..
the basics to wait out the radiation storm.

George
http://cygo.com/