Thanks nette. But for now I just need a rectangle, so template shouldn't be necessary. I actually came across marble city earlier when googling for 'stone hearth london', so will be sure to get a quote from them. Perhaps at a later date I'll go for a "T" shaped piece to lay on top of it. Will probably fit myself... just a matter of ripping out the "placeholder" wood, squirting with adhesive, and lowering into place. In theory.