Tell me at the estimate if a car lift, a floor coating or new plumbing might go in someday, even if it's years off. Those are much easier to plan for before the pour, because once the slab sets, adding them means cutting into it. I'd rather ask now and build the floor for it than have you saw through new concrete later.
On a replacement, we find out why the old floor gave out before we pour a new one. A sunk corner or a crack running toward a downspout usually points to the base or to water, and fresh concrete over the same problem tends to fail the same way. Rebar, the steel set inside the slab, holds the pieces level with each other if a crack does open.
Some garages need work around them too. If you'd like color or a different look rather than plain gray, our decorative concrete work covers that. Where the garage or driveway cuts into a slope and the dirt beside it needs holding back, concrete retaining walls keep that soil from pushing toward the slab.