From the initial post, I imagined a light sheetmetal shed. For your needs, you need double 2x10 rims and middle girder and supported at least 8 feet on center, like a deck. Double 2x8 with supports every 6 feet, but you should check the span chart on that. When doubling 2x, overlap at 1/2 way point. Supports should go down below your frost depth for your area. Looks like other advisers read your question right.
Tools rust, so I would build this tight to the air flow. I would not use garage doors.
Raise the shed at least a foot from the ground and grade it so rain does not pool under the shed.
Truss limits your ceiling height, may be inconvenient working with plywood. You may want to double the floor and ceiling plates to give you few extra inches, and use full length studs.
Depending on your area, all connections may change for the high wind/hurricane codes.
BTW, posts are very easy to dig and install with a rental auger. If you hit a big rock below a frost line, you can use it as a footing.