Honestly, I just faced this very question with designing my new shop. The answer I came up with was to hire a local architect to do it for me.
It simply was not worth my time or the frustration involved to teach myself how to use any of the many different design software programs that are out there, and for $200 I found a local grad doing work on the side and hired him to give me a complete set of plans, 5 sheets, ready to go to Codes with and pull my permits.
It was a good way to directly stimulate the local economy too...the right way!