Oh man thats a tough one. I have a 12X24 that I do woodworking and other things in. Mine has the door in the center of the length of the building. It has 2 3' doors with windows on either side. I am constantly changing things but think I have it now where it best suits me.
All my woodworking tools are on the right side of the building. I keep my planer close to the door (stored under my bench) and use it outside when needed. My table saw is on wheels. I roll it to the door to use it. The thing is to keep sawdust to a minimum inside. (I built a homemade air filter from a small squirrel cage fan and plywood. It hangs from the ceiling and pulls air through a furnace filter. It does a relatively good job of collecting flying dust particles).
On the left side I have a "dirty" bench where I can work on my chainsaw, sharpen mower blades, etc. I also have my garden tools etc. stored on that side as well as lumber storage. I built a loft in this end as well to store stuff above. The key is use the wall space you have for pegboard, shelves or cabinets. Whatever you prefer, but keep your floor as clear as possible to be able to work. Its frustrating and dangerous to have to work around too much stuff in the floor. My router table is a homemade bench top style. I store it under a cabinet. When I need it I can pull it out and put it on top of a bench. My planer is stored under a cabinet as well. The best thing Ive done so far is build a bench from one corner to the door on my woodworking side. Its around 9 foot long. I built sections under with doors and one section with drawers. I can store a lot of stuff under there and that gets it out of the way. I have another bench on the opposite wall of that one that I built with a couple of floor cabinets. My miter saw stays on top. Next to it I have a roll around cart I built and my bench top drill press sits on it.
Over the years I've redone my shop several times. Take a piece of paper and draw out a general layout before you start. Believe me it will help. Don't start piling stuff in it without some idea of where your going with it. You'll change it over time till you get it the way you like it. It only took me about 6 years to get mine where I like it!!!
