Hi student,
               There's a pretty straight-forward way to design a opamp for unity buffer config. Opamp design is simple, you can choose any topology - differential/single-ended / 1stage/2stage OTA design.
          Two important things to keep in mind while designing unity gain buffers are :-
       1. ICMR and OCMR should overlap & should satisy your signal swing specs.
       2. Output CM level & I/p CM level should match / kept in mind while designing.

   Fully Differential topology will allow you to place a good CMFB ckt to control output/input CM level.

   Design of OTA is basic and you can use gm/id methodology for it.

   Pls lemme know if you hv any  further queries.

regards,
Mayank.