You need to complete every Road Racing Series, Dirt Racing Series, Cross Country Series and The Drag Strip race events, including the LEGO Goliath. You need to unlock all the Race Events by completing Brick Challenges (which includes Race Events) to earn bricks to build your house.
I suggest you create a Blueprint, reducing the laps to 1 and with your favourite time of day and weather. You can even create a very short custom route. Or you can use someone else’s Blueprints.
Use your fastest car to cut down on the time each Race Event takes. Make sure you either complete the current Seasonal Events or change them to Normal.
Adjust the difficulty so you are able to Win all the Race Events and you will also get: