We know that we can use the bloch sphere to represent an unitary vectors $v$ in $\mathbb{C}^{2}$, due to the fact $su(2) \approx so(3)$. Then, if we have the function $f:\mathbb{C}^{2} \rightarrow \mathbb{R}$ over vectors $v$ we can declare it as $f(\theta, \phi)$ where $\theta, \phi$ are angles on the bloch sphere. Based on this, the mean value of the function $f$ is $$f_{avg} = \frac{1}{4\pi} \int_{0}^{\pi}f(\theta,\phi)\cdot\sin(\theta) \ d\theta \ d\phi,$$ where $4\pi$ is the solid angle.
The question: If we have the function $g:\mathbb{C}^{4} \rightarrow \mathbb{R}$, how we can to represent the function $g$ using the $n$-sphere angles and how we calculate $g_{avg}$?