Very Easy and inexpesnive, my wife and I did it in about 2 weekends (not including the paint, stain and trim). We built a 1/2 wall with a 1x8 oak board on top, that ties into our stair railing. We have a 3 foot walk way from our existing 2nd floor leading to our 8x8 room above our entry way. I lagged bolted a ledger over the drywall on each side of the foyer, used 2x12 joist hangers and 3/4" plywood floor. We hired carpet installer to install carpet, and a drywall finisher to match existing ceiling. Cost about $1000 bucks for everything about 5 years ago.