If you haven't noticed, the space stations we do build require international cooperation and are basically just a bunch of rocket sections stuck together. The ISS, in all of its glory, took years to assemble and has some serious design constraints.
A project of that magnitude would require lots of highly specialized parts to be launched into orbit first, or, we somehow manage to build an entire fabrication facility in orbit where it can process raw materials.
The concept of a rotating ring is simple. Developing the means to build it is hyper-complex.