A roost is where birds gather to sleep, so dream books read it as rest, belonging and coming home at the end of the day. A crowded roost can also stand for the comfort of a group.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.