Build Your Own Baby Gate. This is great for the bottom of the stairs, or the top, if you used a more child-proof latch design. Maybe just putting the latch on the side the kids aren't supposed to be on would keep little fingers from opening this. I REALLY love how it looks--and it's really just a half door. Perfect.
How to Build a Cheap Storage Shed: Printable plans and a materials list let you build our dollar-savvy storage shed and get great results. http://www.familyhandyman.com/sheds/how-to-build-a-cheap-storage-shed/view-all