[Picus]

A few things I learned having just done this. First, it can be a pain depending on your garage. Second, it can be an even bigger pain depending on your city. The permit for a garage drain into the storm sewers here is $1600. You can run an ABS drain without tearing up all the concrete, but you'll need to find the storm sewer and map out the most efficient route to it; tear up where the drain will be, tear where the sewer is, run the ABS, connect...and if you're lucky and have a straight shot you're done. I was lucky, the storm sewer runs under my garage.

On the grading, if you have better than 4" of concrete you can cut a scupper to the drain, which is essentially a little trough that runs at a 3-5 degree slope to the drain, so even if you don't have a graded pad it'll drain properly.

Another, way less expensive option is to do the scupper thing minus the drain. I've seen a lot of people put two long 2 inch wide by ~1" deep troughs the length of the garage; grade them toward the door and it will carry water out. The only issue there is when you get to the door you have to put the water somewhere where it won't freeze or run a tracer line.