I remember when I was a child, my parents did a pretty good job with our garden. That's how I learn how to do the garden too. You have an unlimited idea and what the designs how you wanted. Besides from not spending money for someone else to do it for you, it's an exercise too both physical and mental.
It is better to do it by yourself if you know how to do it and you know what do you want for your garden. Hiring professionals would be costly. But, if you choose to hire a professional, you have to consider how much budget you have. You can ask or allow them to do the design for you or you can tell them what do you want.
Just remember, no matter what the outcome with your garden as long as you like it and worth the money you spend, that's all matter.