My wife hired a landscape architect a few years ago for her rock garden. We thought it was well worth it. There were a few things he thought of that we never would have, including:
1. Knowledge of SCALE. For example, how large a boulder to place in a particular location given its surroundings.
2. His connections. He knew the best places to buy boulders and plants, and knew people to come in and do them. One of the best things was that the folks work together a lot--so if things don't "look right" they could just say, "Hey, that rock needs to be rotated a bit" to give it the best appearance. My wife NEVER could have done that with ME! They also knew things like, say, what is the largest boulder they can put in without having to bring in a crane (VERY expensive).
3. The landscape architect also has a great knowledge of plants that work in our area--drought resistant, etc.
The end-result was something that is definitely not 'cookie cutter'. My experience is that home computer drafting tools aren't really as easy as they'd like you to think!
For us, it was well worth it, and gave my wife a very suitable garden area that she can enjoy for many years.
Whether or not you choose to use a landscape architect, best of luck on your project! Enjoy!