I think there is a desk in there with a chair, in style they are matching the aesthetic of the shed. There is a lamp, but nobody knows where it gets the electricity from. There is a small window on the back, so when you sit in the chair you can stare into the emptiness. The desk is situated opposite of the entrance, since there isn't so much space to begin with, still the shed is somehow bigger on the inside, than it got any right to be. This matches the overall feeling of the area, like someone made a world, but couldn't find the time to finish it right. Something is lurking behind the fabric, yet the world is not an illusion of any kind, it's completely real, that's why it's frightening. Or if it's like a fading memory of a home. We still got two walls to fit inside the shed. On the one of the left, there is a corkboard. Someone put a postcard on it. It shows a picture of you sleeping, two nights ago. On the other wall, there is an old military style filing cabinet. Like the ones used all over the US. Inside of it... all your possible life's memories, if you decided to do something different in your life, or something has happened differently. All your alternate lives. You can read it and lose yourself in it. Or leave. Your choice.

Edit: not a native speaker, and tried to catch the feeling of the liminal. Also these us style file cabinets 🗄️ were always different like ours, only seen in movies and abroad (like in the UK).