Each "birdscape" is unique and different. Size is not a big concern at all. In fact, it's often a matter of "tweaking" an existing back yard landscape. What matters most is what you put IN the birdscape. Whatever it is, it should lower your dependency on store-bought birdseed.
This blog may spur some ideas. Also, I'd like to help face-to-face. As many of you may know, I'm a licensed Landscape Architect in Texas, and have consulted on the landscape design of hundreds of homes. I can also email you a list of "birdscape" plants that are native to north Texas. Just e-mail me. I've personally seen that these plants are attractive, effective and durable in our climate.
The best time to start planning a birdscape in north Texas is NOW, before springtime and crowds loom around the corner.