This document summarizes discussions from an OA monographs metrics workshop held in October 2019. It discusses recent reports on OA monographs, challenges in developing metrics for both research assessment and informing authors, and results from a survey of OA book authors. The survey found downloads and citations were the most valuable metrics, while Twitter mentions were least valuable. Authors had inflated expectations of what counts as highly cited. The document poses questions about developing technical standards, metrics dashboards, and innovations to make metrics more interesting for researchers.