I have not tested this app but it looks like it’s pretty easy to use and could be useful if you want drawings of existing buildings.
MagicPlan measures the size of the room, draws the floor plan and creates a
DXF file, PDF document, JPEG images and a web site with an interactive floor plan. MagicPlan requires gyroscopes available only with iPhone 4, 4S, the new iPod Touch, the iPad 2 and the new iPad.
If you have tried it please comment below what you think about it.