Truss build the roof and get a rolling gantry crane, it's way more versatile than a fixed beam. I got one that's 10x10 so I can back my trailer and truck under it for loading/unloading and it straddles a parked vehicle when not in use. It also goes under my 12' doors so I can use it outside as well.
Check out Lugnut's shop...I believe his shop is 24x24 so it will give you an idea of what you can do with your 27x28 space. Search the "Tool Box" section for his shop build.
Mike B
