If you decide not simply to adopt but to adapt or create your own OER, there are many good resources to help you get started. We recommend:
The Skyline College CTTL fosters learning about accessibility through resource pages and also provides one-on-one support from instructional designers. As you begin creating or adapting OER, think in particular about students with disabilities; students who use screen readers or other assistive technologies will benefit if you pay attention to hierarchy in your textbook (or other resources), describe images with alt tags, caption your videos and include transcripts, and follow other best practices.
In addition to the CTTL, here are two recommended resources: