If it's on slab, it's not exactly a basement. I think what you are actually asking for is 'studio space'.
As Michael Karas, the concrete contractor is correct...the more concrete you use (ie, full basement) the more the concrete will cost. But the more slab you use, the bigger the footprint of the house, which will cost more in framing, roofing, etc.
The best of both worlds would be to make it a two story house...the first floor being mostly open studio space, second floor your living area.
But I'd strongly consider some other options as well...
- are you building a garage? Make the garage a bit bigger for your 'hobby shop'
- consider an out-building such as a custom shed or a pole barn
- incorporate an extra, larger room in your house plans and just don't put much money into the finishings in it (assuming you'll eventually want to redo it when you sell the house)
what should I call the room on the plans, so that it's governed by the most appropriate codes for what I'm trying to do
This will depend entirely on your local code enforcement/planning office's preferences.
Where I live, we have to mark it as 'storage'.
But, that said...I don't know that you have to label it as anything. Code doesn't typically involve itself with finish. They may require sheetrock, but they don't care what paint you use. They may require a door, but they don't care what trim you use. They likely require a floor, but probably are fine with it being sheets of plywood.