Skinner: I am about 90% through with my garage addition (31x54x12). The width of your's (30') is similar to mine. I have a raised 5' area in front of where the cars will be setting. The raised area is the height of a 2x4 (3 1/2"). I will put tool chests, parts washer, blast cabinet, etc up on this raised area. The slab guys put a small ramp from one level to the other which is pretty neat. I had to go to a roof truss system to carry the 31' span. Good luck on your project. I have had fun with mine.
Mike