In the photo section there's a lot of pics of tanks as they progress. Unfortunately I can't couldn't tell you which posts have those pis, so poke around in the photo section.
Here's a few pointers.
Stay awy from trying to make the tank look symetrical. If that larger piece is going to be your focal point don't put it in dead center, put it off center. The magic ratio is 1.6 to 1. So if you take that 4 ft tank and put that large piece somewhere between 2 feet and 1 foot from one side you'll be getting warmer. Experiment with it. Avoid symetry. Make it look natural. Thats about all I can tell ya. The rest is up to your own creativity.