The Gryffindor Common room was located in my living room. The descriptions from Rowling's books made pretty obvious what I was going to need: squashy chairs, tapestries on the walls, and a roaring fireplace. Easy! I already had squashy chairs; add a few red and gold pillows and call it good.
The fireplace was a different story. While I didn't have a fireplace, I DID have a sizable entertainment center. So I decided to design a disguise for it using a box, stucco printed paper, curtains, mantle decor, and a fireplace DVD. I even found a set of fireplace tools at a yard sale.
I made the chimney by covering a large box with this roll of stucco paper I found at a thrift store. I used the same paper to cover up the top and bottom shelves of my entertainment center. To mask the sides, I hung red and gold curtains from the top of the center. Then I just decorated the top like a mantle and hit 'play' on the DVD and voila! Oddly, everyone agreed that the fake fire really did let off a lot of heat.