I'm looking into building a 24x24 garage,why shouldn't I do a slab for it?
You can post your honest opinion.
First off....Welcome to Garage Journal. Secondly, if you post the state that you live in, it really helps t0 answer questions, as every place has different ways of doing things dependent on the climate.
As far as your question.....if you have a slab, you have to have a bottom plate that sits directly on the slab. Any water can run to the plate and wick up the wood. Chances are you will have a problem on down the road dependent on the climate.
If you have a foundation put in, you can build on top of the foundation, have the foundation a few inches above the slab, or have it a few feet above the slab, and never have to worry about water ruining and of the wood, drywall, or however you finish things off.