While it would be great if you purchased Event Calendar Pro, it was not designed to be a room booking system, at some point I may implement something that would be more suitable for that use case.
You "could" use different instances of Event Calendar Pro to represent rooms but there is not really a way for you to extend it and add features to meet your needs fully. While the source code is available in the Enterprise License, my add on products are not "open source", the license does not allow making derivative works, source code is only available for security audit purposes. So the add on products are not meant t be forked and extended. I will continue to enhance Event Calendar Pro over time but if I make something for booking resources it will be a separate feature. While it would use some similar UI components, conceptually it would work much differently than an event calendar.