  For complex projective smooth surface $X$, let $M$ be the coarse moduli
scheme of rank-two stable sheaves with fixed Chern classes. Grasping the
birational structure of $M$, for example its Kodaira dimension, is a
fundamental problem. However, in the case where $\kappa(X)>0$, the study of
this problem has not necessarily been active in recent years. In this article
we survey the study of this problem, especially for the case where
$\kappa(X)=1$ and $c_1=0$. We will also survey some research on the structure
of singularities of $M$, and a minimal model program of $M$. While explaining
motivations, we raise several unsolved problems.
