This company makes bookshelves to fit in your doorway and make a secret room!
To put screw or nails in the right place, photocopy a template!
DIY Fire Pit: I'm repinning this again because we just bought similar bricks at home depot to make our own firepit! Ours will be slightly bigger, as we got the 12" stones instead of the 8" pictured here. And since we got the bigger stones, ours cost $45, instead of the $30 this blogger paid, but I think it's worth it for the bigger fire pit!
Always Chasing Life: DIY Fire Pit