OK, so this isn't a tutorial, but a few people here may find this handy.
It is a FREE web based drawing package, which was designed for but not exclusively dedicated to drawing floor plans. This could be handy for drawing maps or other things like top down shooter games that take place indoors?
Anyway, check it out... it's FREE and seems pretty powerful.
http://draw.labs.autodesk.com/ADDraw/draw.html
~Sol