Putting down a new ceramic-tile or wood floor? You'll probably have to trim the door casings so the tiles or floorboards fit beneath. Here's how professional remodelers do it: Place a tile or floorboard upside down in front of the casing as a thickness gauge. Then lay a handsaw on top of the flooring material and trim off the bottom of the casing. Turning the flooring upside down keeps the saw teeth from scratching it.