I just went through a whole lot of pain to add a drain after the fact. I would love to be in your shoes as snow/salt/slush is a reality here in Northern Ontario as well.
In your shoes, I would add drains in the center of each parking "stall", and have your concrete guys slope to that. This should avoid puddles in the morning that you'll be walking through. My shop slopes to the side, 1" over 16' which definitely has all the water going to the side wall, but is not noticeable. Either drain to a drywell dug below frost line outside your shop, or tie in to municipal with a grease trap. I just did a RaceDeck parking pad, which contains water and directs to the added drain. The drain tiles are very nice as they elevates the floor surface 1/2" above the slope. Adding an grease trap doesn't have to be big deal..one fellow here made his own out of concrete which passed inspection.
You have a great opportunity to do it right, from the get go. Rebar will be your friend, along with expansion joints. If I was doing a new garage, I'd be very tempted to lower the areas where the cars will park by 1/2", and drop drain tiles into the drainage "pit" so your floor would appear flush, but you'd never step in puddles. You could create this effect also by ceramic tiling the floor, but leaving the park areas bare sealed concrete..same effect. In other words, a floor like this where the tiles were flush to the rest of the floor.