A garden shed is a small retreat and a place for tools, read as practical skills and private time for yourself. Something hidden in the shed stands for an overlooked resource or memory.
When this appeared in your dream, what were you feeling?
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.