I have an older version of Broaderbund Home Design 5.1 I use it for homes and floorplans, but I also used it for my shop. I draw the walls, put in the doors and windows, then select from the tools for furniture to place in the space so I can get a feel of how the space will work. I can drag the furniture around, change what direction it faces and even make it smaller or bigger. For a shop, or any space, I can select a table and change the dimensions to anything I want. To figure out where my table saw would go, I just placed a table where I thougth it might fit. Then I put other tables around for benches and storage areas. I can label each table anything that I want it to represent.
As a contractor, this has really been helpful with clients who want me to build something, but are unsure on how big they need it, or how their stuff will fit in the space. I did a storage shed over the summer that I created about a dozen different versions of how they could arrange their stuff and then added other features to it. They liked the biggest fanciest version, which meant a bigger job for me, and more money. Being able to offer the different versions for them to look at was invaluable.
I've also found that it takes several tries and versions to get the best possible layout. Once you draw it out and think you have it right, ask others for their input. There is always something that you will forget, and the more you can put into your plan, the cheaper it is to do the earlier you can plan for it. Sometimes it's really something obvious and silly, other times it's something unique that you didn't even know you wanted. A good example is with me is that I forgot to add a shop sink to my workshop. I had one in my last workshop and used it every day. It's something I absolutley wanted, but forgot about while working on layout, electrical plugs, lighting and door placement. In fact, it wasn't until I was running drain lines that my Mom asked about the shop sink.
Good luck,
Eddie