I could find few things on migrating the rooms (resources) however I was wondering how how could migrated users in forest A access the resources in forest B.
ForestA: exchange 2013 - new AD (forest)
ForestB: exchange 2010 - old AD (forest)
namespace is shared so emails are AnB@email.com
Users in forest A can see calendar free/busy in forest B as I have two way trust.