It's actually really easy to do. Just remember paint to make it look 100 times better.
Step 1: Work out shapes/sizes/etc that you want.
Step 2: Cut the shapes out of polystyrene - (Tip: Use a hacksaw blade, from one of the handheld saws, heat it up on the cooker hob for a few seconds and it slices like butter)
Step 3: Arrange all the pieces and use some form of adhesive (Some people use cocktail sticks) to stick them together
Step 4: Get the tile grout and pick a place to start. Apply the grout randomly (i.e not in a uniform strict style) to get a natural effect, It's also good to use some expanding foam around the edges for an even nicer finish.
Good luck with the project.
