"Flagstone" Floor:  After seeing the simulated flagstone plans in Brian Nickoll's book, I decided to try my hand.  I am really pleased with the results.  The flagstone tiles are actually the back side of Formica chips (the ones found in the home improvement stores for sample colors).

How To Do It: Cut the chips into pieces.  For a rustic look a good size is 1" x 1-1/2" ; I used 3/4" x 3/4".  I taped about 20 together and cut them all at once.  Another way is to score them with a ruler and a blade or other scoring instrument and snap on the line.

Sand around the edge of each tile to give it a slightly irregular shape.  This is best done with a power grinding disk.  I fix mounted my Dremel to a stand in order to have both hands free.  Be sure to wear eye protection and a mask -- this creates a lot of dust!!

Using a good quality adhesive or contact cement, glue the chips, colored side down.  It's a good idea to make a template of the room on thin wood or cardboard and mount the tiles on the base material.  That way you can remove the floor at a later time and you won't have to do the sanding inside the house.  A staggered tile pattern is the most popular but you can do a traditional grid or diamond pattern if the tiles are all the same size.

After floor has completely dried, grout using joint compound tinted with a small amount of black acrylic paint to get the dark grey color.   Spread the compound evenly with a putty knife, allow a couple of minutes for it to set up, and then wipe away excess with a slightly damp sponge.  Allow grout to dry for several hours or overnight.  If there are any cracks in the joints or low spots, repeat with another layer of compound and let dry once more.

Sand the complete floor so that it is even and level.  I used a power palm sander as the hand method would have been very tiring.  Then seal with 1-2 coats of satin varnish, rubbing with fine steel wool between  coats.  You can also use a colorant in the stain or mix some water-based stain with water-based polyurethane to get a striking effect to the tiles.