I am going to need to build a workshop in the yard of the house I recently bought, probably next spring. My income is solely derived from stuff I make in a workshop, and the house is under 1000 square feet so I can't put it in there. My plan is to build a workshop that can be easily converted into a garage by the future owner of the house if they wish. I anticipate living in this house for 1-5 years or so and eventually building a house and workshop on a larger lot with more room for gardening and selling this house.
I've been thinking of something in the two car garage size range with an upstairs that I would use for 'clean' jobs, packing shipments, and storage. The town allows monolithic slabs, and being in the Adirondacks I imagine the frost line is pretty deep, maybe 4 feet. If I had a monolithic slab poured 20x24 would it be feasible to use 2x12x20 on 16" centers to support the upstairs floor, or is that too big of a span for joists? Is there another kind of floor support beam I could use without a center post that would be better?
Another alternative is to make something like 24x24 with attic trusses and a monolithic slab. I have never built with trusses and am not fond of them because of the way they chop up the space under the roof and make it much less useful, and also they are expensive, but the cheaper foundation might offset the truss cost.
A third alternative I have thought of is to have a real foundation with a footer, wall and floating slab. If this was 24x24 I could put a footer in the center for a support post, add a beam down the center and use 12' 2x10 or 2x12 for joists. I don't know how much of a disadvantage it would be in a garage to have a center post instead of a clear span.
If anyone has any experiences with these methods or suggestions about what I should build I will be very grateful for advice. I have built a number of outbuildings here on the farm where I currently live, but the big two have interior posts to support the upper floor. The largest one I built was 6 years ago, and is 28x48 with a tall loft, so the scale of this building is not daunting to me, but I have never built or even lived with a garage so I am doubtful as to the parameters for them. Thank you very much for taking time to read this.