We did something like this with another shape we were trying - make your initial in Word or another publishing software - print it to "poster size" and make the size of the poster the size of the letter you want. After it prints on 6 sheets or whatever it takes to print out poster sized, trace it onto styro or those sculpting sheets of oasis. We've never made the letters, but this procedure from some of our UK friends in a thread about shaped funeral pieces has helped us immensely.I think we are really old fashioned but we use a wall projector (from an art supply store) choose a font the bride likes or that we like if bride can't make up her mind (U would be shocked at how often this happens) print the initials, lay them on the projector, and instead of projecting on the wall we project on to a correct size piece of foam.
trace using dots, cut out initial and got at it withthe flowers.