advice on levelling a garage floor

I have converted my garage into a rumpus and want to tile the floor but the cement starts sloping 3 meters from the roller door opening to be about 20-30mm lower where it meets the driveway. I gather this was to let the water run out after driving a wet car into the garage.

Whats the cheapest option to level it as using self leveling compound is going to use a bucketload of bags if my calculations are correct...

How do I stop what ever I use from running out onto the driveway?


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